diff --git a/src/generators/dom/index.ts b/src/generators/dom/index.ts
index e103f428cf..acf161642d 100644
--- a/src/generators/dom/index.ts
+++ b/src/generators/dom/index.ts
@@ -123,7 +123,7 @@ export default function dom(
 
 			const condition = `${deps.map(dep => `changed.${dep}`).join(' || ')}`;
 
-			const statement = `if (@differs(state.${key}, (state.${key} = %computed-${key}(${deps
+			const statement = `if (this._differs(state.${key}, (state.${key} = %computed-${key}(${deps
 				.map(dep => `state.${dep}`)
 				.join(', ')})))) changed.${key} = true;`;
 
@@ -208,6 +208,7 @@ export default function dom(
 		${options.dev && !generator.customElement &&
 			`if (!options || (!options.target && !options.root)) throw new Error("'target' is a required option");`}
 		@init(this, options);
+		this._differs = @differs;
 		${templateProperties.store && `this.store = %store();`}
 		${generator.usesRefs && `this.refs = {};`}
 		this._state = @assign(${initialState.join(', ')});
diff --git a/src/shared/index.js b/src/shared/index.js
index ec8706be6d..0005569532 100644
--- a/src/shared/index.js
+++ b/src/shared/index.js
@@ -26,25 +26,11 @@ export function destroyDev(detach) {
 }
 
 export function differs(a, b) {
-	if (a == null || b == null) return a !== b;
-	if (a.constructor !== b.constructor) return true;
-	if (a.valueOf && b.valueOf) {
-		a = a.valueOf();
-		b = b.valueOf();
-	}
-	if (typeof a === 'number' && isNaN(a) && isNaN(b)) return false;
-	return a !== b || typeof a === 'object' || typeof a === 'function';
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 export function differsImmutable(a, b) {
-	if (a == null || b == null) return a !== b;
-	if (a.constructor !== b.constructor) return true;
-	if (a.valueOf && b.valueOf) {
-		a = a.valueOf();
-		b = b.valueOf();
-	}
-	if (typeof a === 'number' && isNaN(a) && isNaN(b)) return false;
-	return a !== b;
+	return a != a ? b == b : a !== b;
 }
 
 export function dispatchObservers(component, group, changed, newState, oldState) {
@@ -168,28 +154,7 @@ export function _set(newState) {
 		dirty = false;
 
 	for (var key in newState) {
-		if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
-	}
-	if (!dirty) return;
-
-	this._state = assign({}, oldState, newState);
-	this._recompute(changed, this._state);
-	if (this._bind) this._bind(changed, this._state);
-
-	if (this._fragment) {
-		dispatchObservers(this, this._observers.pre, changed, this._state, oldState);
-		this._fragment.p(changed, this._state);
-		dispatchObservers(this, this._observers.post, changed, this._state, oldState);
-	}
-}
-
-export function _setImmutable(newState) {
-	var oldState = this._state,
-		changed = {},
-		dirty = false;
-
-	for (var key in newState) {
-		if (differsImmutable(newState[key], oldState[key])) changed[key] = dirty = true;
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
 	}
 	if (!dirty) return;
 
diff --git a/test/js/samples/collapses-text-around-comments/expected-bundle.js b/test/js/samples/collapses-text-around-comments/expected-bundle.js
index ffc75c872c..ba89e7777b 100644
--- a/test/js/samples/collapses-text-around-comments/expected-bundle.js
+++ b/test/js/samples/collapses-text-around-comments/expected-bundle.js
@@ -52,14 +52,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	if (a == null || b == null) return a !== b;
-	if (a.constructor !== b.constructor) return true;
-	if (a.valueOf && b.valueOf) {
-		a = a.valueOf();
-		b = b.valueOf();
-	}
-	if (typeof a === 'number' && isNaN(a) && isNaN(b)) return false;
-	return a !== b || typeof a === 'object' || typeof a === 'function';
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -158,7 +151,7 @@ function _set(newState) {
 		dirty = false;
 
 	for (var key in newState) {
-		if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
 	}
 	if (!dirty) return;
 
@@ -250,6 +243,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign(data(), options.data);
 
 	if (!document.getElementById("svelte-2794052100-style")) add_css();
diff --git a/test/js/samples/collapses-text-around-comments/expected.js b/test/js/samples/collapses-text-around-comments/expected.js
index aea4721e36..a76fb36edf 100644
--- a/test/js/samples/collapses-text-around-comments/expected.js
+++ b/test/js/samples/collapses-text-around-comments/expected.js
@@ -1,5 +1,5 @@
 /* generated by Svelte vX.Y.Z */
-import { appendNode, assign, createElement, createText, detachNode, init, insertNode, noop, proto, setAttribute } from "svelte/shared.js";
+import { appendNode, assign, createElement, createText, detachNode, differs, init, insertNode, noop, proto, setAttribute } from "svelte/shared.js";
 
 function data() {
 	return { foo: 42 }
@@ -51,6 +51,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign(data(), options.data);
 
 	if (!document.getElementById("svelte-2794052100-style")) add_css();
diff --git a/test/js/samples/component-static/expected-bundle.js b/test/js/samples/component-static/expected-bundle.js
index 970b8e139a..b28b38ddb6 100644
--- a/test/js/samples/component-static/expected-bundle.js
+++ b/test/js/samples/component-static/expected-bundle.js
@@ -28,14 +28,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	if (a == null || b == null) return a !== b;
-	if (a.constructor !== b.constructor) return true;
-	if (a.valueOf && b.valueOf) {
-		a = a.valueOf();
-		b = b.valueOf();
-	}
-	if (typeof a === 'number' && isNaN(a) && isNaN(b)) return false;
-	return a !== b || typeof a === 'object' || typeof a === 'function';
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -134,7 +127,7 @@ function _set(newState) {
 		dirty = false;
 
 	for (var key in newState) {
-		if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
 	}
 	if (!dirty) return;
 
@@ -208,6 +201,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	if (!options.root) {
diff --git a/test/js/samples/component-static/expected.js b/test/js/samples/component-static/expected.js
index d75cce1253..de06c6fb2d 100644
--- a/test/js/samples/component-static/expected.js
+++ b/test/js/samples/component-static/expected.js
@@ -1,5 +1,5 @@
 /* generated by Svelte vX.Y.Z */
-import { assign, callAll, init, noop, proto } from "svelte/shared.js";
+import { assign, callAll, differs, init, noop, proto } from "svelte/shared.js";
 
 var Nested = window.Nested;
 
@@ -33,6 +33,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	if (!options.root) {
diff --git a/test/js/samples/computed-collapsed-if-immutable/_config.js b/test/js/samples/computed-collapsed-if-immutable/_config.js
new file mode 100644
index 0000000000..06713941e0
--- /dev/null
+++ b/test/js/samples/computed-collapsed-if-immutable/_config.js
@@ -0,0 +1,5 @@
+export default {
+	options: {
+		immutable: true
+	}
+};
\ No newline at end of file
diff --git a/test/js/samples/computed-collapsed-if-immutable/expected-bundle.js b/test/js/samples/computed-collapsed-if-immutable/expected-bundle.js
new file mode 100644
index 0000000000..509aa9328f
--- /dev/null
+++ b/test/js/samples/computed-collapsed-if-immutable/expected-bundle.js
@@ -0,0 +1,218 @@
+function noop() {}
+
+function assign(target) {
+	var k,
+		source,
+		i = 1,
+		len = arguments.length;
+	for (; i < len; i++) {
+		source = arguments[i];
+		for (k in source) target[k] = source[k];
+	}
+
+	return target;
+}
+
+function blankObject() {
+	return Object.create(null);
+}
+
+function destroy(detach) {
+	this.destroy = noop;
+	this.fire('destroy');
+	this.set = this.get = noop;
+
+	if (detach !== false) this._fragment.u();
+	this._fragment.d();
+	this._fragment = this._state = null;
+}
+
+function differsImmutable(a, b) {
+	return a != a ? b == b : a !== b;
+}
+
+function dispatchObservers(component, group, changed, newState, oldState) {
+	for (var key in group) {
+		if (!changed[key]) continue;
+
+		var newValue = newState[key];
+		var oldValue = oldState[key];
+
+		var callbacks = group[key];
+		if (!callbacks) continue;
+
+		for (var i = 0; i < callbacks.length; i += 1) {
+			var callback = callbacks[i];
+			if (callback.__calling) continue;
+
+			callback.__calling = true;
+			callback.call(component, newValue, oldValue);
+			callback.__calling = false;
+		}
+	}
+}
+
+function fire(eventName, data) {
+	var handlers =
+		eventName in this._handlers && this._handlers[eventName].slice();
+	if (!handlers) return;
+
+	for (var i = 0; i < handlers.length; i += 1) {
+		handlers[i].call(this, data);
+	}
+}
+
+function get(key) {
+	return key ? this._state[key] : this._state;
+}
+
+function init(component, options) {
+	component._observers = { pre: blankObject(), post: blankObject() };
+	component._handlers = blankObject();
+	component._bind = options._bind;
+
+	component.options = options;
+	component.root = options.root || component;
+	component.store = component.root.store || options.store;
+}
+
+function observe(key, callback, options) {
+	var group = options && options.defer
+		? this._observers.post
+		: this._observers.pre;
+
+	(group[key] || (group[key] = [])).push(callback);
+
+	if (!options || options.init !== false) {
+		callback.__calling = true;
+		callback.call(this, this._state[key]);
+		callback.__calling = false;
+	}
+
+	return {
+		cancel: function() {
+			var index = group[key].indexOf(callback);
+			if (~index) group[key].splice(index, 1);
+		}
+	};
+}
+
+function on(eventName, handler) {
+	if (eventName === 'teardown') return this.on('destroy', handler);
+
+	var handlers = this._handlers[eventName] || (this._handlers[eventName] = []);
+	handlers.push(handler);
+
+	return {
+		cancel: function() {
+			var index = handlers.indexOf(handler);
+			if (~index) handlers.splice(index, 1);
+		}
+	};
+}
+
+function set(newState) {
+	this._set(assign({}, newState));
+	if (this.root._lock) return;
+	this.root._lock = true;
+	callAll(this.root._beforecreate);
+	callAll(this.root._oncreate);
+	callAll(this.root._aftercreate);
+	this.root._lock = false;
+}
+
+function _set(newState) {
+	var oldState = this._state,
+		changed = {},
+		dirty = false;
+
+	for (var key in newState) {
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
+	}
+	if (!dirty) return;
+
+	this._state = assign({}, oldState, newState);
+	this._recompute(changed, this._state);
+	if (this._bind) this._bind(changed, this._state);
+
+	if (this._fragment) {
+		dispatchObservers(this, this._observers.pre, changed, this._state, oldState);
+		this._fragment.p(changed, this._state);
+		dispatchObservers(this, this._observers.post, changed, this._state, oldState);
+	}
+}
+
+function callAll(fns) {
+	while (fns && fns.length) fns.shift()();
+}
+
+function _mount(target, anchor) {
+	this._fragment.m(target, anchor);
+}
+
+function _unmount() {
+	if (this._fragment) this._fragment.u();
+}
+
+var proto = {
+	destroy: destroy,
+	get: get,
+	fire: fire,
+	observe: observe,
+	on: on,
+	set: set,
+	teardown: destroy,
+	_recompute: noop,
+	_set: _set,
+	_mount: _mount,
+	_unmount: _unmount
+};
+
+/* generated by Svelte vX.Y.Z */
+function a(x) {
+	return x * 2;
+}
+
+function b(x) {
+	return x * 3;
+}
+
+function create_main_fragment(state, component) {
+
+	return {
+		c: noop,
+
+		m: noop,
+
+		p: noop,
+
+		u: noop,
+
+		d: noop
+	};
+}
+
+function SvelteComponent(options) {
+	init(this, options);
+	this._differs = differsImmutable;
+	this._state = assign({}, options.data);
+	this._recompute({ x: 1 }, this._state);
+
+	this._fragment = create_main_fragment(this._state, this);
+
+	if (options.target) {
+		this._fragment.c();
+		this._fragment.m(options.target, options.anchor || null);
+	}
+}
+
+assign(SvelteComponent.prototype, proto);
+
+SvelteComponent.prototype._recompute = function _recompute(changed, state) {
+	if (changed.x) {
+		if (this._differs(state.a, (state.a = a(state.x)))) changed.a = true;
+		if (this._differs(state.b, (state.b = b(state.x)))) changed.b = true;
+	}
+};
+
+export default SvelteComponent;
diff --git a/test/js/samples/computed-collapsed-if-immutable/expected.js b/test/js/samples/computed-collapsed-if-immutable/expected.js
new file mode 100644
index 0000000000..b5beba1695
--- /dev/null
+++ b/test/js/samples/computed-collapsed-if-immutable/expected.js
@@ -0,0 +1,49 @@
+/* generated by Svelte vX.Y.Z */
+import { assign, differsImmutable, init, noop, proto } from "svelte/shared.js";
+
+function a(x) {
+	return x * 2;
+}
+
+function b(x) {
+	return x * 3;
+}
+
+function create_main_fragment(state, component) {
+
+	return {
+		c: noop,
+
+		m: noop,
+
+		p: noop,
+
+		u: noop,
+
+		d: noop
+	};
+}
+
+function SvelteComponent(options) {
+	init(this, options);
+	this._differs = differsImmutable;
+	this._state = assign({}, options.data);
+	this._recompute({ x: 1 }, this._state);
+
+	this._fragment = create_main_fragment(this._state, this);
+
+	if (options.target) {
+		this._fragment.c();
+		this._fragment.m(options.target, options.anchor || null);
+	}
+}
+
+assign(SvelteComponent.prototype, proto);
+
+SvelteComponent.prototype._recompute = function _recompute(changed, state) {
+	if (changed.x) {
+		if (this._differs(state.a, (state.a = a(state.x)))) changed.a = true;
+		if (this._differs(state.b, (state.b = b(state.x)))) changed.b = true;
+	}
+}
+export default SvelteComponent;
\ No newline at end of file
diff --git a/test/js/samples/computed-collapsed-if-immutable/input.html b/test/js/samples/computed-collapsed-if-immutable/input.html
new file mode 100644
index 0000000000..a68513b860
--- /dev/null
+++ b/test/js/samples/computed-collapsed-if-immutable/input.html
@@ -0,0 +1,8 @@
+<script>
+	export default {
+		computed: {
+			a: x => x * 2,
+			b: x => x * 3
+		}
+	};
+</script>
\ No newline at end of file
diff --git a/test/js/samples/computed-collapsed-if/expected-bundle.js b/test/js/samples/computed-collapsed-if/expected-bundle.js
index e9285f3bc0..475b5d3491 100644
--- a/test/js/samples/computed-collapsed-if/expected-bundle.js
+++ b/test/js/samples/computed-collapsed-if/expected-bundle.js
@@ -28,14 +28,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	if (a == null || b == null) return a !== b;
-	if (a.constructor !== b.constructor) return true;
-	if (a.valueOf && b.valueOf) {
-		a = a.valueOf();
-		b = b.valueOf();
-	}
-	if (typeof a === 'number' && isNaN(a) && isNaN(b)) return false;
-	return a !== b || typeof a === 'object' || typeof a === 'function';
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -134,7 +127,7 @@ function _set(newState) {
 		dirty = false;
 
 	for (var key in newState) {
-		if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
 	}
 	if (!dirty) return;
 
@@ -201,6 +194,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 	this._recompute({ x: 1 }, this._state);
 
@@ -216,8 +210,8 @@ assign(SvelteComponent.prototype, proto);
 
 SvelteComponent.prototype._recompute = function _recompute(changed, state) {
 	if (changed.x) {
-		if (differs(state.a, (state.a = a(state.x)))) changed.a = true;
-		if (differs(state.b, (state.b = b(state.x)))) changed.b = true;
+		if (this._differs(state.a, (state.a = a(state.x)))) changed.a = true;
+		if (this._differs(state.b, (state.b = b(state.x)))) changed.b = true;
 	}
 };
 
diff --git a/test/js/samples/computed-collapsed-if/expected.js b/test/js/samples/computed-collapsed-if/expected.js
index c2f5e3c2be..c0765a4115 100644
--- a/test/js/samples/computed-collapsed-if/expected.js
+++ b/test/js/samples/computed-collapsed-if/expected.js
@@ -26,6 +26,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 	this._recompute({ x: 1 }, this._state);
 
@@ -41,8 +42,8 @@ assign(SvelteComponent.prototype, proto);
 
 SvelteComponent.prototype._recompute = function _recompute(changed, state) {
 	if (changed.x) {
-		if (differs(state.a, (state.a = a(state.x)))) changed.a = true;
-		if (differs(state.b, (state.b = b(state.x)))) changed.b = true;
+		if (this._differs(state.a, (state.a = a(state.x)))) changed.a = true;
+		if (this._differs(state.b, (state.b = b(state.x)))) changed.b = true;
 	}
 }
 export default SvelteComponent;
\ No newline at end of file
diff --git a/test/js/samples/css-media-query/expected-bundle.js b/test/js/samples/css-media-query/expected-bundle.js
index 6ccc9200d5..cfed183001 100644
--- a/test/js/samples/css-media-query/expected-bundle.js
+++ b/test/js/samples/css-media-query/expected-bundle.js
@@ -48,14 +48,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	if (a == null || b == null) return a !== b;
-	if (a.constructor !== b.constructor) return true;
-	if (a.valueOf && b.valueOf) {
-		a = a.valueOf();
-		b = b.valueOf();
-	}
-	if (typeof a === 'number' && isNaN(a) && isNaN(b)) return false;
-	return a !== b || typeof a === 'object' || typeof a === 'function';
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -154,7 +147,7 @@ function _set(newState) {
 		dirty = false;
 
 	for (var key in newState) {
-		if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
 	}
 	if (!dirty) return;
 
@@ -236,6 +229,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	if (!document.getElementById("svelte-3905933315-style")) add_css();
diff --git a/test/js/samples/css-media-query/expected.js b/test/js/samples/css-media-query/expected.js
index 37afa6b42a..61e78032e8 100644
--- a/test/js/samples/css-media-query/expected.js
+++ b/test/js/samples/css-media-query/expected.js
@@ -1,5 +1,5 @@
 /* generated by Svelte vX.Y.Z */
-import { appendNode, assign, createElement, detachNode, init, insertNode, noop, proto, setAttribute } from "svelte/shared.js";
+import { appendNode, assign, createElement, detachNode, differs, init, insertNode, noop, proto, setAttribute } from "svelte/shared.js";
 
 function encapsulateStyles(node) {
 	setAttribute(node, "svelte-3905933315", "");
@@ -41,6 +41,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	if (!document.getElementById("svelte-3905933315-style")) add_css();
diff --git a/test/js/samples/css-shadow-dom-keyframes/expected-bundle.js b/test/js/samples/css-shadow-dom-keyframes/expected-bundle.js
index 4948afea4d..2684f5ddb7 100644
--- a/test/js/samples/css-shadow-dom-keyframes/expected-bundle.js
+++ b/test/js/samples/css-shadow-dom-keyframes/expected-bundle.js
@@ -40,14 +40,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	if (a == null || b == null) return a !== b;
-	if (a.constructor !== b.constructor) return true;
-	if (a.valueOf && b.valueOf) {
-		a = a.valueOf();
-		b = b.valueOf();
-	}
-	if (typeof a === 'number' && isNaN(a) && isNaN(b)) return false;
-	return a !== b || typeof a === 'object' || typeof a === 'function';
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -146,7 +139,7 @@ function _set(newState) {
 		dirty = false;
 
 	for (var key in newState) {
-		if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
 	}
 	if (!dirty) return;
 
@@ -216,6 +209,7 @@ class SvelteComponent extends HTMLElement {
 	constructor(options = {}) {
 		super();
 		init(this, options);
+		this._differs = differs;
 		this._state = assign({}, options.data);
 
 		this.attachShadow({ mode: 'open' });
diff --git a/test/js/samples/css-shadow-dom-keyframes/expected.js b/test/js/samples/css-shadow-dom-keyframes/expected.js
index 496586e632..de4528ff0e 100644
--- a/test/js/samples/css-shadow-dom-keyframes/expected.js
+++ b/test/js/samples/css-shadow-dom-keyframes/expected.js
@@ -1,5 +1,5 @@
 /* generated by Svelte vX.Y.Z */
-import { assign, createElement, detachNode, init, insertNode, noop, proto } from "svelte/shared.js";
+import { assign, createElement, detachNode, differs, init, insertNode, noop, proto } from "svelte/shared.js";
 
 function create_main_fragment(state, component) {
 	var div;
@@ -29,6 +29,7 @@ class SvelteComponent extends HTMLElement {
 	constructor(options = {}) {
 		super();
 		init(this, options);
+		this._differs = differs;
 		this._state = assign({}, options.data);
 
 		this.attachShadow({ mode: 'open' });
diff --git a/test/js/samples/deconflict-globals/expected-bundle.js b/test/js/samples/deconflict-globals/expected-bundle.js
index 6733b68767..b3e979c0e9 100644
--- a/test/js/samples/deconflict-globals/expected-bundle.js
+++ b/test/js/samples/deconflict-globals/expected-bundle.js
@@ -28,14 +28,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	if (a == null || b == null) return a !== b;
-	if (a.constructor !== b.constructor) return true;
-	if (a.valueOf && b.valueOf) {
-		a = a.valueOf();
-		b = b.valueOf();
-	}
-	if (typeof a === 'number' && isNaN(a) && isNaN(b)) return false;
-	return a !== b || typeof a === 'object' || typeof a === 'function';
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -134,7 +127,7 @@ function _set(newState) {
 		dirty = false;
 
 	for (var key in newState) {
-		if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
 	}
 	if (!dirty) return;
 
@@ -203,6 +196,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign(data_1(), options.data);
 
 	var _oncreate = oncreate.bind(this);
diff --git a/test/js/samples/deconflict-globals/expected.js b/test/js/samples/deconflict-globals/expected.js
index 8730f4e3c3..95da7a1a0c 100644
--- a/test/js/samples/deconflict-globals/expected.js
+++ b/test/js/samples/deconflict-globals/expected.js
@@ -1,5 +1,5 @@
 /* generated by Svelte vX.Y.Z */
-import { assign, callAll, init, noop, proto } from "svelte/shared.js";
+import { assign, callAll, differs, init, noop, proto } from "svelte/shared.js";
 
 function data_1() {
 	return {
@@ -28,6 +28,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign(data_1(), options.data);
 
 	var _oncreate = oncreate.bind(this);
diff --git a/test/js/samples/do-use-dataset/expected-bundle.js b/test/js/samples/do-use-dataset/expected-bundle.js
index 442afd002e..8974c8a808 100644
--- a/test/js/samples/do-use-dataset/expected-bundle.js
+++ b/test/js/samples/do-use-dataset/expected-bundle.js
@@ -44,14 +44,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	if (a == null || b == null) return a !== b;
-	if (a.constructor !== b.constructor) return true;
-	if (a.valueOf && b.valueOf) {
-		a = a.valueOf();
-		b = b.valueOf();
-	}
-	if (typeof a === 'number' && isNaN(a) && isNaN(b)) return false;
-	return a !== b || typeof a === 'object' || typeof a === 'function';
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -150,7 +143,7 @@ function _set(newState) {
 		dirty = false;
 
 	for (var key in newState) {
-		if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
 	}
 	if (!dirty) return;
 
@@ -232,6 +225,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/do-use-dataset/expected.js b/test/js/samples/do-use-dataset/expected.js
index 1ae7417469..cbe6e9ac2b 100644
--- a/test/js/samples/do-use-dataset/expected.js
+++ b/test/js/samples/do-use-dataset/expected.js
@@ -1,5 +1,5 @@
 /* generated by Svelte vX.Y.Z */
-import { assign, createElement, createText, detachNode, init, insertNode, noop, proto } from "svelte/shared.js";
+import { assign, createElement, createText, detachNode, differs, init, insertNode, noop, proto } from "svelte/shared.js";
 
 function create_main_fragment(state, component) {
 	var div, text, div_1;
@@ -41,6 +41,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/dont-use-dataset-in-legacy/expected-bundle.js b/test/js/samples/dont-use-dataset-in-legacy/expected-bundle.js
index 3b5681f2ca..9f546da356 100644
--- a/test/js/samples/dont-use-dataset-in-legacy/expected-bundle.js
+++ b/test/js/samples/dont-use-dataset-in-legacy/expected-bundle.js
@@ -48,14 +48,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	if (a == null || b == null) return a !== b;
-	if (a.constructor !== b.constructor) return true;
-	if (a.valueOf && b.valueOf) {
-		a = a.valueOf();
-		b = b.valueOf();
-	}
-	if (typeof a === 'number' && isNaN(a) && isNaN(b)) return false;
-	return a !== b || typeof a === 'object' || typeof a === 'function';
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -154,7 +147,7 @@ function _set(newState) {
 		dirty = false;
 
 	for (var key in newState) {
-		if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
 	}
 	if (!dirty) return;
 
@@ -236,6 +229,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/dont-use-dataset-in-legacy/expected.js b/test/js/samples/dont-use-dataset-in-legacy/expected.js
index 03eef26ced..989b1a47f8 100644
--- a/test/js/samples/dont-use-dataset-in-legacy/expected.js
+++ b/test/js/samples/dont-use-dataset-in-legacy/expected.js
@@ -1,5 +1,5 @@
 /* generated by Svelte vX.Y.Z */
-import { assign, createElement, createText, detachNode, init, insertNode, noop, proto, setAttribute } from "svelte/shared.js";
+import { assign, createElement, createText, detachNode, differs, init, insertNode, noop, proto, setAttribute } from "svelte/shared.js";
 
 function create_main_fragment(state, component) {
 	var div, text, div_1;
@@ -41,6 +41,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/dont-use-dataset-in-svg/expected-bundle.js b/test/js/samples/dont-use-dataset-in-svg/expected-bundle.js
index 242ac51828..e6c5fee0c6 100644
--- a/test/js/samples/dont-use-dataset-in-svg/expected-bundle.js
+++ b/test/js/samples/dont-use-dataset-in-svg/expected-bundle.js
@@ -48,14 +48,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	if (a == null || b == null) return a !== b;
-	if (a.constructor !== b.constructor) return true;
-	if (a.valueOf && b.valueOf) {
-		a = a.valueOf();
-		b = b.valueOf();
-	}
-	if (typeof a === 'number' && isNaN(a) && isNaN(b)) return false;
-	return a !== b || typeof a === 'object' || typeof a === 'function';
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -154,7 +147,7 @@ function _set(newState) {
 		dirty = false;
 
 	for (var key in newState) {
-		if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
 	}
 	if (!dirty) return;
 
@@ -234,6 +227,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/dont-use-dataset-in-svg/expected.js b/test/js/samples/dont-use-dataset-in-svg/expected.js
index b87f152298..f96da75975 100644
--- a/test/js/samples/dont-use-dataset-in-svg/expected.js
+++ b/test/js/samples/dont-use-dataset-in-svg/expected.js
@@ -1,5 +1,5 @@
 /* generated by Svelte vX.Y.Z */
-import { appendNode, assign, createSvgElement, detachNode, init, insertNode, noop, proto, setAttribute } from "svelte/shared.js";
+import { appendNode, assign, createSvgElement, detachNode, differs, init, insertNode, noop, proto, setAttribute } from "svelte/shared.js";
 
 function create_main_fragment(state, component) {
 	var svg, g, g_1;
@@ -39,6 +39,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/each-block-changed-check/expected-bundle.js b/test/js/samples/each-block-changed-check/expected-bundle.js
index ca09f3774f..428e9c739a 100644
--- a/test/js/samples/each-block-changed-check/expected-bundle.js
+++ b/test/js/samples/each-block-changed-check/expected-bundle.js
@@ -60,14 +60,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	if (a == null || b == null) return a !== b;
-	if (a.constructor !== b.constructor) return true;
-	if (a.valueOf && b.valueOf) {
-		a = a.valueOf();
-		b = b.valueOf();
-	}
-	if (typeof a === 'number' && isNaN(a) && isNaN(b)) return false;
-	return a !== b || typeof a === 'object' || typeof a === 'function';
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -166,7 +159,7 @@ function _set(newState) {
 		dirty = false;
 
 	for (var key in newState) {
-		if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
 	}
 	if (!dirty) return;
 
@@ -348,6 +341,7 @@ function create_each_block(state, comments, comment, i, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/each-block-changed-check/expected.js b/test/js/samples/each-block-changed-check/expected.js
index 29a57322e0..c436550f07 100644
--- a/test/js/samples/each-block-changed-check/expected.js
+++ b/test/js/samples/each-block-changed-check/expected.js
@@ -1,5 +1,5 @@
 /* generated by Svelte vX.Y.Z */
-import { appendNode, assign, createElement, createText, destroyEach, detachAfter, detachNode, init, insertNode, noop, proto } from "svelte/shared.js";
+import { appendNode, assign, createElement, createText, destroyEach, detachAfter, detachNode, differs, init, insertNode, noop, proto } from "svelte/shared.js";
 
 function create_main_fragment(state, component) {
 	var text, p, text_1;
@@ -141,6 +141,7 @@ function create_each_block(state, comments, comment, i, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/event-handlers-custom/expected-bundle.js b/test/js/samples/event-handlers-custom/expected-bundle.js
index f9e32a0256..819b653caa 100644
--- a/test/js/samples/event-handlers-custom/expected-bundle.js
+++ b/test/js/samples/event-handlers-custom/expected-bundle.js
@@ -40,14 +40,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	if (a == null || b == null) return a !== b;
-	if (a.constructor !== b.constructor) return true;
-	if (a.valueOf && b.valueOf) {
-		a = a.valueOf();
-		b = b.valueOf();
-	}
-	if (typeof a === 'number' && isNaN(a) && isNaN(b)) return false;
-	return a !== b || typeof a === 'object' || typeof a === 'function';
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -146,7 +139,7 @@ function _set(newState) {
 		dirty = false;
 
 	for (var key in newState) {
-		if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
 	}
 	if (!dirty) return;
 
@@ -233,6 +226,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/event-handlers-custom/expected.js b/test/js/samples/event-handlers-custom/expected.js
index f7862efb62..1d5ae4b17e 100644
--- a/test/js/samples/event-handlers-custom/expected.js
+++ b/test/js/samples/event-handlers-custom/expected.js
@@ -1,5 +1,5 @@
 /* generated by Svelte vX.Y.Z */
-import { assign, createElement, detachNode, init, insertNode, noop, proto } from "svelte/shared.js";
+import { assign, createElement, detachNode, differs, init, insertNode, noop, proto } from "svelte/shared.js";
 
 function foo( node, callback ) {
 	// code goes here
@@ -46,6 +46,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/head-no-whitespace/expected-bundle.js b/test/js/samples/head-no-whitespace/expected-bundle.js
index 62aac217d5..398617dd13 100644
--- a/test/js/samples/head-no-whitespace/expected-bundle.js
+++ b/test/js/samples/head-no-whitespace/expected-bundle.js
@@ -40,14 +40,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	if (a == null || b == null) return a !== b;
-	if (a.constructor !== b.constructor) return true;
-	if (a.valueOf && b.valueOf) {
-		a = a.valueOf();
-		b = b.valueOf();
-	}
-	if (typeof a === 'number' && isNaN(a) && isNaN(b)) return false;
-	return a !== b || typeof a === 'object' || typeof a === 'function';
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -146,7 +139,7 @@ function _set(newState) {
 		dirty = false;
 
 	for (var key in newState) {
-		if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
 	}
 	if (!dirty) return;
 
@@ -223,6 +216,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/head-no-whitespace/expected.js b/test/js/samples/head-no-whitespace/expected.js
index 32a1a5da88..d9bee61c62 100644
--- a/test/js/samples/head-no-whitespace/expected.js
+++ b/test/js/samples/head-no-whitespace/expected.js
@@ -1,5 +1,5 @@
 /* generated by Svelte vX.Y.Z */
-import { appendNode, assign, createElement, detachNode, init, noop, proto } from "svelte/shared.js";
+import { appendNode, assign, createElement, detachNode, differs, init, noop, proto } from "svelte/shared.js";
 
 function create_main_fragment(state, component) {
 	var meta, meta_1;
@@ -36,6 +36,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/if-block-no-update/expected-bundle.js b/test/js/samples/if-block-no-update/expected-bundle.js
index 681edc072e..b3dc0c6b13 100644
--- a/test/js/samples/if-block-no-update/expected-bundle.js
+++ b/test/js/samples/if-block-no-update/expected-bundle.js
@@ -44,14 +44,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	if (a == null || b == null) return a !== b;
-	if (a.constructor !== b.constructor) return true;
-	if (a.valueOf && b.valueOf) {
-		a = a.valueOf();
-		b = b.valueOf();
-	}
-	if (typeof a === 'number' && isNaN(a) && isNaN(b)) return false;
-	return a !== b || typeof a === 'object' || typeof a === 'function';
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -150,7 +143,7 @@ function _set(newState) {
 		dirty = false;
 
 	for (var key in newState) {
-		if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
 	}
 	if (!dirty) return;
 
@@ -281,6 +274,7 @@ function select_block_type(state) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/if-block-no-update/expected.js b/test/js/samples/if-block-no-update/expected.js
index 8f030e4e53..59c54d1ad7 100644
--- a/test/js/samples/if-block-no-update/expected.js
+++ b/test/js/samples/if-block-no-update/expected.js
@@ -1,5 +1,5 @@
 /* generated by Svelte vX.Y.Z */
-import { assign, createComment, createElement, detachNode, init, insertNode, noop, proto } from "svelte/shared.js";
+import { assign, createComment, createElement, detachNode, differs, init, insertNode, noop, proto } from "svelte/shared.js";
 
 function create_main_fragment(state, component) {
 	var if_block_anchor;
@@ -90,6 +90,7 @@ function select_block_type(state) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/if-block-simple/expected-bundle.js b/test/js/samples/if-block-simple/expected-bundle.js
index 9ce6331f44..9dac6d03a9 100644
--- a/test/js/samples/if-block-simple/expected-bundle.js
+++ b/test/js/samples/if-block-simple/expected-bundle.js
@@ -44,14 +44,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	if (a == null || b == null) return a !== b;
-	if (a.constructor !== b.constructor) return true;
-	if (a.valueOf && b.valueOf) {
-		a = a.valueOf();
-		b = b.valueOf();
-	}
-	if (typeof a === 'number' && isNaN(a) && isNaN(b)) return false;
-	return a !== b || typeof a === 'object' || typeof a === 'function';
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -150,7 +143,7 @@ function _set(newState) {
 		dirty = false;
 
 	for (var key in newState) {
-		if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
 	}
 	if (!dirty) return;
 
@@ -257,6 +250,7 @@ function create_if_block(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/if-block-simple/expected.js b/test/js/samples/if-block-simple/expected.js
index 0b9fbece70..667640451f 100644
--- a/test/js/samples/if-block-simple/expected.js
+++ b/test/js/samples/if-block-simple/expected.js
@@ -1,5 +1,5 @@
 /* generated by Svelte vX.Y.Z */
-import { assign, createComment, createElement, detachNode, init, insertNode, noop, proto } from "svelte/shared.js";
+import { assign, createComment, createElement, detachNode, differs, init, insertNode, noop, proto } from "svelte/shared.js";
 
 function create_main_fragment(state, component) {
 	var if_block_anchor;
@@ -66,6 +66,7 @@ function create_if_block(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/inline-style-optimized-multiple/expected-bundle.js b/test/js/samples/inline-style-optimized-multiple/expected-bundle.js
index 9077eea9d7..8843db047b 100644
--- a/test/js/samples/inline-style-optimized-multiple/expected-bundle.js
+++ b/test/js/samples/inline-style-optimized-multiple/expected-bundle.js
@@ -44,14 +44,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	if (a == null || b == null) return a !== b;
-	if (a.constructor !== b.constructor) return true;
-	if (a.valueOf && b.valueOf) {
-		a = a.valueOf();
-		b = b.valueOf();
-	}
-	if (typeof a === 'number' && isNaN(a) && isNaN(b)) return false;
-	return a !== b || typeof a === 'object' || typeof a === 'function';
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -150,7 +143,7 @@ function _set(newState) {
 		dirty = false;
 
 	for (var key in newState) {
-		if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
 	}
 	if (!dirty) return;
 
@@ -230,6 +223,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/inline-style-optimized-multiple/expected.js b/test/js/samples/inline-style-optimized-multiple/expected.js
index 77173460e2..0b0aca132b 100644
--- a/test/js/samples/inline-style-optimized-multiple/expected.js
+++ b/test/js/samples/inline-style-optimized-multiple/expected.js
@@ -1,5 +1,5 @@
 /* generated by Svelte vX.Y.Z */
-import { assign, createElement, detachNode, init, insertNode, noop, proto, setStyle } from "svelte/shared.js";
+import { assign, createElement, detachNode, differs, init, insertNode, noop, proto, setStyle } from "svelte/shared.js";
 
 function create_main_fragment(state, component) {
 	var div;
@@ -39,6 +39,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/inline-style-optimized-url/expected-bundle.js b/test/js/samples/inline-style-optimized-url/expected-bundle.js
index 7277ff587a..e88379a4e4 100644
--- a/test/js/samples/inline-style-optimized-url/expected-bundle.js
+++ b/test/js/samples/inline-style-optimized-url/expected-bundle.js
@@ -44,14 +44,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	if (a == null || b == null) return a !== b;
-	if (a.constructor !== b.constructor) return true;
-	if (a.valueOf && b.valueOf) {
-		a = a.valueOf();
-		b = b.valueOf();
-	}
-	if (typeof a === 'number' && isNaN(a) && isNaN(b)) return false;
-	return a !== b || typeof a === 'object' || typeof a === 'function';
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -150,7 +143,7 @@ function _set(newState) {
 		dirty = false;
 
 	for (var key in newState) {
-		if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
 	}
 	if (!dirty) return;
 
@@ -225,6 +218,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/inline-style-optimized-url/expected.js b/test/js/samples/inline-style-optimized-url/expected.js
index bed00356f6..1d8d5c467a 100644
--- a/test/js/samples/inline-style-optimized-url/expected.js
+++ b/test/js/samples/inline-style-optimized-url/expected.js
@@ -1,5 +1,5 @@
 /* generated by Svelte vX.Y.Z */
-import { assign, createElement, detachNode, init, insertNode, noop, proto, setStyle } from "svelte/shared.js";
+import { assign, createElement, detachNode, differs, init, insertNode, noop, proto, setStyle } from "svelte/shared.js";
 
 function create_main_fragment(state, component) {
 	var div;
@@ -34,6 +34,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/inline-style-optimized/expected-bundle.js b/test/js/samples/inline-style-optimized/expected-bundle.js
index 9b3f41768f..a1b8278e87 100644
--- a/test/js/samples/inline-style-optimized/expected-bundle.js
+++ b/test/js/samples/inline-style-optimized/expected-bundle.js
@@ -44,14 +44,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	if (a == null || b == null) return a !== b;
-	if (a.constructor !== b.constructor) return true;
-	if (a.valueOf && b.valueOf) {
-		a = a.valueOf();
-		b = b.valueOf();
-	}
-	if (typeof a === 'number' && isNaN(a) && isNaN(b)) return false;
-	return a !== b || typeof a === 'object' || typeof a === 'function';
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -150,7 +143,7 @@ function _set(newState) {
 		dirty = false;
 
 	for (var key in newState) {
-		if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
 	}
 	if (!dirty) return;
 
@@ -225,6 +218,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/inline-style-optimized/expected.js b/test/js/samples/inline-style-optimized/expected.js
index 7f873e296c..7f4f19248b 100644
--- a/test/js/samples/inline-style-optimized/expected.js
+++ b/test/js/samples/inline-style-optimized/expected.js
@@ -1,5 +1,5 @@
 /* generated by Svelte vX.Y.Z */
-import { assign, createElement, detachNode, init, insertNode, noop, proto, setStyle } from "svelte/shared.js";
+import { assign, createElement, detachNode, differs, init, insertNode, noop, proto, setStyle } from "svelte/shared.js";
 
 function create_main_fragment(state, component) {
 	var div;
@@ -34,6 +34,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/inline-style-unoptimized/expected-bundle.js b/test/js/samples/inline-style-unoptimized/expected-bundle.js
index f1a5a53d7f..9db0da26fe 100644
--- a/test/js/samples/inline-style-unoptimized/expected-bundle.js
+++ b/test/js/samples/inline-style-unoptimized/expected-bundle.js
@@ -44,14 +44,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	if (a == null || b == null) return a !== b;
-	if (a.constructor !== b.constructor) return true;
-	if (a.valueOf && b.valueOf) {
-		a = a.valueOf();
-		b = b.valueOf();
-	}
-	if (typeof a === 'number' && isNaN(a) && isNaN(b)) return false;
-	return a !== b || typeof a === 'object' || typeof a === 'function';
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -150,7 +143,7 @@ function _set(newState) {
 		dirty = false;
 
 	for (var key in newState) {
-		if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
 	}
 	if (!dirty) return;
 
@@ -236,6 +229,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/inline-style-unoptimized/expected.js b/test/js/samples/inline-style-unoptimized/expected.js
index 4c4d38d2bf..0e53480fe8 100644
--- a/test/js/samples/inline-style-unoptimized/expected.js
+++ b/test/js/samples/inline-style-unoptimized/expected.js
@@ -1,5 +1,5 @@
 /* generated by Svelte vX.Y.Z */
-import { assign, createElement, createText, detachNode, init, insertNode, noop, proto } from "svelte/shared.js";
+import { assign, createElement, createText, detachNode, differs, init, insertNode, noop, proto } from "svelte/shared.js";
 
 function create_main_fragment(state, component) {
 	var div, text, div_1, div_1_style_value;
@@ -45,6 +45,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/input-without-blowback-guard/expected-bundle.js b/test/js/samples/input-without-blowback-guard/expected-bundle.js
index b32377763e..fb3f125b00 100644
--- a/test/js/samples/input-without-blowback-guard/expected-bundle.js
+++ b/test/js/samples/input-without-blowback-guard/expected-bundle.js
@@ -48,14 +48,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	if (a == null || b == null) return a !== b;
-	if (a.constructor !== b.constructor) return true;
-	if (a.valueOf && b.valueOf) {
-		a = a.valueOf();
-		b = b.valueOf();
-	}
-	if (typeof a === 'number' && isNaN(a) && isNaN(b)) return false;
-	return a !== b || typeof a === 'object' || typeof a === 'function';
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -154,7 +147,7 @@ function _set(newState) {
 		dirty = false;
 
 	for (var key in newState) {
-		if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
 	}
 	if (!dirty) return;
 
@@ -236,6 +229,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/input-without-blowback-guard/expected.js b/test/js/samples/input-without-blowback-guard/expected.js
index 03f27ab6d9..9342b25ec9 100644
--- a/test/js/samples/input-without-blowback-guard/expected.js
+++ b/test/js/samples/input-without-blowback-guard/expected.js
@@ -1,5 +1,5 @@
 /* generated by Svelte vX.Y.Z */
-import { addListener, assign, createElement, detachNode, init, insertNode, proto, removeListener } from "svelte/shared.js";
+import { addListener, assign, createElement, detachNode, differs, init, insertNode, proto, removeListener } from "svelte/shared.js";
 
 function create_main_fragment(state, component) {
 	var input;
@@ -41,6 +41,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/legacy-input-type/expected-bundle.js b/test/js/samples/legacy-input-type/expected-bundle.js
index 1dbd32f619..8b6e2faa8f 100644
--- a/test/js/samples/legacy-input-type/expected-bundle.js
+++ b/test/js/samples/legacy-input-type/expected-bundle.js
@@ -46,14 +46,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	if (a == null || b == null) return a !== b;
-	if (a.constructor !== b.constructor) return true;
-	if (a.valueOf && b.valueOf) {
-		a = a.valueOf();
-		b = b.valueOf();
-	}
-	if (typeof a === 'number' && isNaN(a) && isNaN(b)) return false;
-	return a !== b || typeof a === 'object' || typeof a === 'function';
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -152,7 +145,7 @@ function _set(newState) {
 		dirty = false;
 
 	for (var key in newState) {
-		if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
 	}
 	if (!dirty) return;
 
@@ -223,6 +216,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/legacy-input-type/expected.js b/test/js/samples/legacy-input-type/expected.js
index 719f550044..22d71f036d 100644
--- a/test/js/samples/legacy-input-type/expected.js
+++ b/test/js/samples/legacy-input-type/expected.js
@@ -1,5 +1,5 @@
 /* generated by Svelte vX.Y.Z */
-import { assign, createElement, detachNode, init, insertNode, noop, proto, setInputType } from "svelte/shared.js";
+import { assign, createElement, detachNode, differs, init, insertNode, noop, proto, setInputType } from "svelte/shared.js";
 
 function create_main_fragment(state, component) {
 	var input;
@@ -30,6 +30,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/legacy-quote-class/expected-bundle.js b/test/js/samples/legacy-quote-class/expected-bundle.js
index 0b203fb4b6..b4900a16b5 100644
--- a/test/js/samples/legacy-quote-class/expected-bundle.js
+++ b/test/js/samples/legacy-quote-class/expected-bundle.js
@@ -63,14 +63,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	if (a == null || b == null) return a !== b;
-	if (a.constructor !== b.constructor) return true;
-	if (a.valueOf && b.valueOf) {
-		a = a.valueOf();
-		b = b.valueOf();
-	}
-	if (typeof a === 'number' && isNaN(a) && isNaN(b)) return false;
-	return a !== b || typeof a === 'object' || typeof a === 'function';
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -169,7 +162,7 @@ function _set(newState) {
 		dirty = false;
 
 	for (var key in newState) {
-		if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
 	}
 	if (!dirty) return;
 
@@ -248,6 +241,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/legacy-quote-class/expected.js b/test/js/samples/legacy-quote-class/expected.js
index 0b49103c47..c4421f91cd 100644
--- a/test/js/samples/legacy-quote-class/expected.js
+++ b/test/js/samples/legacy-quote-class/expected.js
@@ -1,5 +1,5 @@
 /* generated by Svelte vX.Y.Z */
-import { assign, children, claimElement, createElement, detachNode, init, insertNode, noop, proto } from "svelte/shared.js";
+import { assign, children, claimElement, createElement, detachNode, differs, init, insertNode, noop, proto } from "svelte/shared.js";
 
 function create_main_fragment(state, component) {
 	var div;
@@ -38,6 +38,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/media-bindings/expected-bundle.js b/test/js/samples/media-bindings/expected-bundle.js
index ec971167be..2eacb53f8c 100644
--- a/test/js/samples/media-bindings/expected-bundle.js
+++ b/test/js/samples/media-bindings/expected-bundle.js
@@ -56,14 +56,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	if (a == null || b == null) return a !== b;
-	if (a.constructor !== b.constructor) return true;
-	if (a.valueOf && b.valueOf) {
-		a = a.valueOf();
-		b = b.valueOf();
-	}
-	if (typeof a === 'number' && isNaN(a) && isNaN(b)) return false;
-	return a !== b || typeof a === 'object' || typeof a === 'function';
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -162,7 +155,7 @@ function _set(newState) {
 		dirty = false;
 
 	for (var key in newState) {
-		if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
 	}
 	if (!dirty) return;
 
@@ -289,6 +282,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	if (!options.root) {
diff --git a/test/js/samples/media-bindings/expected.js b/test/js/samples/media-bindings/expected.js
index ae80f288f6..503228ce06 100644
--- a/test/js/samples/media-bindings/expected.js
+++ b/test/js/samples/media-bindings/expected.js
@@ -1,5 +1,5 @@
 /* generated by Svelte vX.Y.Z */
-import { addListener, assign, callAll, createElement, detachNode, init, insertNode, proto, removeListener, timeRangesToArray } from "svelte/shared.js";
+import { addListener, assign, callAll, createElement, detachNode, differs, init, insertNode, proto, removeListener, timeRangesToArray } from "svelte/shared.js";
 
 function create_main_fragment(state, component) {
 	var audio, audio_is_paused = true, audio_updating = false, audio_animationframe;
@@ -86,6 +86,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	if (!options.root) {
diff --git a/test/js/samples/non-imported-component/expected-bundle.js b/test/js/samples/non-imported-component/expected-bundle.js
index 46de1d757e..9cba5b8bfb 100644
--- a/test/js/samples/non-imported-component/expected-bundle.js
+++ b/test/js/samples/non-imported-component/expected-bundle.js
@@ -42,14 +42,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	if (a == null || b == null) return a !== b;
-	if (a.constructor !== b.constructor) return true;
-	if (a.valueOf && b.valueOf) {
-		a = a.valueOf();
-		b = b.valueOf();
-	}
-	if (typeof a === 'number' && isNaN(a) && isNaN(b)) return false;
-	return a !== b || typeof a === 'object' || typeof a === 'function';
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -148,7 +141,7 @@ function _set(newState) {
 		dirty = false;
 
 	for (var key in newState) {
-		if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
 	}
 	if (!dirty) return;
 
@@ -231,6 +224,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	if (!options.root) {
diff --git a/test/js/samples/non-imported-component/expected.js b/test/js/samples/non-imported-component/expected.js
index e7fc2c7255..c35b4f88a7 100644
--- a/test/js/samples/non-imported-component/expected.js
+++ b/test/js/samples/non-imported-component/expected.js
@@ -1,5 +1,5 @@
 /* generated by Svelte vX.Y.Z */
-import { assign, callAll, createText, detachNode, init, insertNode, noop, proto } from "svelte/shared.js";
+import { assign, callAll, createText, detachNode, differs, init, insertNode, noop, proto } from "svelte/shared.js";
 import Imported from 'Imported.html';
 
 
@@ -45,6 +45,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	if (!options.root) {
diff --git a/test/js/samples/onrender-onteardown-rewritten/expected-bundle.js b/test/js/samples/onrender-onteardown-rewritten/expected-bundle.js
index b65e0bfc2a..26f52231fc 100644
--- a/test/js/samples/onrender-onteardown-rewritten/expected-bundle.js
+++ b/test/js/samples/onrender-onteardown-rewritten/expected-bundle.js
@@ -28,14 +28,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	if (a == null || b == null) return a !== b;
-	if (a.constructor !== b.constructor) return true;
-	if (a.valueOf && b.valueOf) {
-		a = a.valueOf();
-		b = b.valueOf();
-	}
-	if (typeof a === 'number' && isNaN(a) && isNaN(b)) return false;
-	return a !== b || typeof a === 'object' || typeof a === 'function';
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -134,7 +127,7 @@ function _set(newState) {
 		dirty = false;
 
 	for (var key in newState) {
-		if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
 	}
 	if (!dirty) return;
 
@@ -197,6 +190,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._handlers.destroy = [ondestroy];
diff --git a/test/js/samples/onrender-onteardown-rewritten/expected.js b/test/js/samples/onrender-onteardown-rewritten/expected.js
index 51763c0b00..02203f83c0 100644
--- a/test/js/samples/onrender-onteardown-rewritten/expected.js
+++ b/test/js/samples/onrender-onteardown-rewritten/expected.js
@@ -1,5 +1,5 @@
 /* generated by Svelte vX.Y.Z */
-import { assign, callAll, init, noop, proto } from "svelte/shared.js";
+import { assign, callAll, differs, init, noop, proto } from "svelte/shared.js";
 
 function oncreate() {};
 
@@ -22,6 +22,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._handlers.destroy = [ondestroy];
diff --git a/test/js/samples/setup-method/expected-bundle.js b/test/js/samples/setup-method/expected-bundle.js
index 80bb847692..103bf174ac 100644
--- a/test/js/samples/setup-method/expected-bundle.js
+++ b/test/js/samples/setup-method/expected-bundle.js
@@ -28,14 +28,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	if (a == null || b == null) return a !== b;
-	if (a.constructor !== b.constructor) return true;
-	if (a.valueOf && b.valueOf) {
-		a = a.valueOf();
-		b = b.valueOf();
-	}
-	if (typeof a === 'number' && isNaN(a) && isNaN(b)) return false;
-	return a !== b || typeof a === 'object' || typeof a === 'function';
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -134,7 +127,7 @@ function _set(newState) {
 		dirty = false;
 
 	for (var key in newState) {
-		if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
 	}
 	if (!dirty) return;
 
@@ -209,6 +202,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/setup-method/expected.js b/test/js/samples/setup-method/expected.js
index 092a32ed3b..5b306a12e7 100644
--- a/test/js/samples/setup-method/expected.js
+++ b/test/js/samples/setup-method/expected.js
@@ -1,5 +1,5 @@
 /* generated by Svelte vX.Y.Z */
-import { assign, init, noop, proto } from "svelte/shared.js";
+import { assign, differs, init, noop, proto } from "svelte/shared.js";
 
 var methods = {
 	foo ( bar ) {
@@ -34,6 +34,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/svg-title/expected-bundle.js b/test/js/samples/svg-title/expected-bundle.js
index 1ee4d64a48..2050f6dcfe 100644
--- a/test/js/samples/svg-title/expected-bundle.js
+++ b/test/js/samples/svg-title/expected-bundle.js
@@ -48,14 +48,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	if (a == null || b == null) return a !== b;
-	if (a.constructor !== b.constructor) return true;
-	if (a.valueOf && b.valueOf) {
-		a = a.valueOf();
-		b = b.valueOf();
-	}
-	if (typeof a === 'number' && isNaN(a) && isNaN(b)) return false;
-	return a !== b || typeof a === 'object' || typeof a === 'function';
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -154,7 +147,7 @@ function _set(newState) {
 		dirty = false;
 
 	for (var key in newState) {
-		if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
 	}
 	if (!dirty) return;
 
@@ -224,6 +217,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/svg-title/expected.js b/test/js/samples/svg-title/expected.js
index 39ccf227c0..6c5d08ca00 100644
--- a/test/js/samples/svg-title/expected.js
+++ b/test/js/samples/svg-title/expected.js
@@ -1,5 +1,5 @@
 /* generated by Svelte vX.Y.Z */
-import { appendNode, assign, createSvgElement, createText, detachNode, init, insertNode, noop, proto } from "svelte/shared.js";
+import { appendNode, assign, createSvgElement, createText, detachNode, differs, init, insertNode, noop, proto } from "svelte/shared.js";
 
 function create_main_fragment(state, component) {
 	var svg, title, text;
@@ -29,6 +29,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/title/expected-bundle.js b/test/js/samples/title/expected-bundle.js
index 454a1fad0e..2fcc0b6197 100644
--- a/test/js/samples/title/expected-bundle.js
+++ b/test/js/samples/title/expected-bundle.js
@@ -28,14 +28,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	if (a == null || b == null) return a !== b;
-	if (a.constructor !== b.constructor) return true;
-	if (a.valueOf && b.valueOf) {
-		a = a.valueOf();
-		b = b.valueOf();
-	}
-	if (typeof a === 'number' && isNaN(a) && isNaN(b)) return false;
-	return a !== b || typeof a === 'object' || typeof a === 'function';
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -134,7 +127,7 @@ function _set(newState) {
 		dirty = false;
 
 	for (var key in newState) {
-		if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
 	}
 	if (!dirty) return;
 
@@ -200,6 +193,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/title/expected.js b/test/js/samples/title/expected.js
index 6aa903d25e..e15441fbdc 100644
--- a/test/js/samples/title/expected.js
+++ b/test/js/samples/title/expected.js
@@ -1,5 +1,5 @@
 /* generated by Svelte vX.Y.Z */
-import { assign, init, noop, proto } from "svelte/shared.js";
+import { assign, differs, init, noop, proto } from "svelte/shared.js";
 
 function create_main_fragment(state, component) {
 	var title_value;
@@ -25,6 +25,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/use-elements-as-anchors/expected-bundle.js b/test/js/samples/use-elements-as-anchors/expected-bundle.js
index 9ac57fe215..e22e431d53 100644
--- a/test/js/samples/use-elements-as-anchors/expected-bundle.js
+++ b/test/js/samples/use-elements-as-anchors/expected-bundle.js
@@ -52,14 +52,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	if (a == null || b == null) return a !== b;
-	if (a.constructor !== b.constructor) return true;
-	if (a.valueOf && b.valueOf) {
-		a = a.valueOf();
-		b = b.valueOf();
-	}
-	if (typeof a === 'number' && isNaN(a) && isNaN(b)) return false;
-	return a !== b || typeof a === 'object' || typeof a === 'function';
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -158,7 +151,7 @@ function _set(newState) {
 		dirty = false;
 
 	for (var key in newState) {
-		if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
 	}
 	if (!dirty) return;
 
@@ -447,6 +440,7 @@ function create_if_block_4(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/use-elements-as-anchors/expected.js b/test/js/samples/use-elements-as-anchors/expected.js
index d2609c45b0..0b45ca8679 100644
--- a/test/js/samples/use-elements-as-anchors/expected.js
+++ b/test/js/samples/use-elements-as-anchors/expected.js
@@ -1,5 +1,5 @@
 /* generated by Svelte vX.Y.Z */
-import { appendNode, assign, createComment, createElement, createText, detachNode, init, insertNode, noop, proto } from "svelte/shared.js";
+import { appendNode, assign, createComment, createElement, createText, detachNode, differs, init, insertNode, noop, proto } from "svelte/shared.js";
 
 function create_main_fragment(state, component) {
 	var div, text, p, text_2, text_3, text_4, p_1, text_6, text_8, if_block_4_anchor;
@@ -248,6 +248,7 @@ function create_if_block_4(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 
 	this._fragment = create_main_fragment(this._state, this);
diff --git a/test/js/samples/window-binding-scroll/expected-bundle.js b/test/js/samples/window-binding-scroll/expected-bundle.js
index 457f6d55ea..97231f4bb6 100644
--- a/test/js/samples/window-binding-scroll/expected-bundle.js
+++ b/test/js/samples/window-binding-scroll/expected-bundle.js
@@ -48,14 +48,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	if (a == null || b == null) return a !== b;
-	if (a.constructor !== b.constructor) return true;
-	if (a.valueOf && b.valueOf) {
-		a = a.valueOf();
-		b = b.valueOf();
-	}
-	if (typeof a === 'number' && isNaN(a) && isNaN(b)) return false;
-	return a !== b || typeof a === 'object' || typeof a === 'function';
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -154,7 +147,7 @@ function _set(newState) {
 		dirty = false;
 
 	for (var key in newState) {
-		if (differs(newState[key], oldState[key])) changed[key] = dirty = true;
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
 	}
 	if (!dirty) return;
 
@@ -248,6 +241,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 	this._state.y = window.scrollY;
 
diff --git a/test/js/samples/window-binding-scroll/expected.js b/test/js/samples/window-binding-scroll/expected.js
index 70eae003d7..55bc0eb53a 100644
--- a/test/js/samples/window-binding-scroll/expected.js
+++ b/test/js/samples/window-binding-scroll/expected.js
@@ -1,5 +1,5 @@
 /* generated by Svelte vX.Y.Z */
-import { appendNode, assign, createElement, createText, detachNode, init, insertNode, proto } from "svelte/shared.js";
+import { appendNode, assign, createElement, createText, detachNode, differs, init, insertNode, proto } from "svelte/shared.js";
 
 function create_main_fragment(state, component) {
 	var window_updating = false, clear_window_updating = function() { window_updating = false; }, window_updating_timeout, p, text, text_1;
@@ -53,6 +53,7 @@ function create_main_fragment(state, component) {
 
 function SvelteComponent(options) {
 	init(this, options);
+	this._differs = differs;
 	this._state = assign({}, options.data);
 	this._state.y = window.scrollY;
 
diff --git a/test/store/index.js b/test/store/index.js
index d8053367a9..e3c024e4d5 100644
--- a/test/store/index.js
+++ b/test/store/index.js
@@ -187,4 +187,44 @@ describe('store', () => {
 			}, /Cyclical dependency detected/);
 		});
 	});
+
+	describe('immutable', () => {
+		it('observing state only changes on immutable updates', () => {
+			let newFoo;
+			let oldFoo;
+			let callCount = 0;
+			let value1 = {};
+			let value2 = {};
+
+			const store = new Store({
+				foo: value1
+			}, { immutable: true });
+
+			store.observe('foo', (n, o) => {
+				callCount++;
+				newFoo = n;
+				oldFoo = o;
+			});
+
+			assert.equal(callCount, 1);
+			assert.equal(newFoo, value1);
+			assert.equal(oldFoo, undefined);
+
+			store.set({
+				foo: value1
+			});
+
+			assert.equal(callCount, 1);
+			assert.equal(newFoo, value1);
+			assert.equal(oldFoo, undefined);
+
+			store.set({
+				foo: value2
+			});
+
+			assert.equal(callCount, 2);
+			assert.equal(newFoo, value2);
+			assert.equal(oldFoo, value1);
+		});
+	});
 });