diff --git a/src/generators/Generator.ts b/src/generators/Generator.ts
index 1f48424c95..35bb2e9859 100644
--- a/src/generators/Generator.ts
+++ b/src/generators/Generator.ts
@@ -626,6 +626,10 @@ export default class Generator {
 					addDeclaration('store', templateProperties.store.value);
 				}
 
+				if (templateProperties.immutable) {
+					addDeclaration('immutable', templateProperties.immutable.value);
+				}
+
 				if (templateProperties.tag) {
 					this.tag = templateProperties.tag.value.value;
 				}
diff --git a/src/generators/dom/index.ts b/src/generators/dom/index.ts
index 08bdf0012f..5f91cb5123 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 +208,10 @@ 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);
+		${options.immutable && deindent`
+			if (options.immutable !== undefined ? options.immutable : ${templateProperties.immutable && '%immutable' || 'this.root.options.immutable'}) {
+				this._differs = @differsImmutable;
+			}`}
 		${templateProperties.store && `this.store = %store();`}
 		${generator.usesRefs && `this.refs = {};`}
 		this._state = @assign(${initialState.join(', ')});
diff --git a/src/interfaces.ts b/src/interfaces.ts
index 9773d330d3..82de8cd047 100644
--- a/src/interfaces.ts
+++ b/src/interfaces.ts
@@ -52,6 +52,7 @@ export interface CompileOptions {
 	cssOutputFilename?: string;
 
 	dev?: boolean;
+	immutable?: boolean;
 	shared?: boolean | string;
 	cascade?: boolean;
 	hydratable?: boolean;
diff --git a/src/shared/index.js b/src/shared/index.js
index ef160ebf07..8996ee378a 100644
--- a/src/shared/index.js
+++ b/src/shared/index.js
@@ -26,7 +26,11 @@ export function destroyDev(detach) {
 }
 
 export function differs(a, b) {
-	return a !== b || ((a && 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) {
+	return a != a ? b == b : a !== b;
 }
 
 export function dispatchObservers(component, group, changed, newState, oldState) {
@@ -68,6 +72,7 @@ export function init(component, options) {
 	component._observers = { pre: blankObject(), post: blankObject() };
 	component._handlers = blankObject();
 	component._bind = options._bind;
+	component._differs = differs;
 
 	component.options = options;
 	component.root = options.root || component;
@@ -150,7 +155,7 @@ export 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;
 
diff --git a/src/validate/js/propValidators/immutable.ts b/src/validate/js/propValidators/immutable.ts
new file mode 100644
index 0000000000..b54521d9e4
--- /dev/null
+++ b/src/validate/js/propValidators/immutable.ts
@@ -0,0 +1,11 @@
+import { Validator } from '../../';
+import { Node } from '../../../interfaces';
+
+export default function immutable(validator: Validator, prop: Node) {
+	if (prop.value.type !== 'Literal' || typeof prop.value.value !== 'boolean') {
+		validator.error(
+			`'immutable' must be a boolean literal`,
+			prop.value.start
+		);
+	}
+}
diff --git a/src/validate/js/propValidators/index.ts b/src/validate/js/propValidators/index.ts
index 942c757601..05819b0837 100644
--- a/src/validate/js/propValidators/index.ts
+++ b/src/validate/js/propValidators/index.ts
@@ -15,6 +15,7 @@ import tag from './tag';
 import transitions from './transitions';
 import setup from './setup';
 import store from './store';
+import immutable from './immutable';
 
 export default {
 	data,
@@ -34,4 +35,5 @@ export default {
 	transitions,
 	setup,
 	store,
+	immutable,
 };
diff --git a/store.js b/store.js
index f31c659080..853d36a52a 100644
--- a/store.js
+++ b/store.js
@@ -2,12 +2,13 @@ import {
 	assign,
 	blankObject,
 	differs,
+	differsImmutable,
 	dispatchObservers,
 	get,
 	observe
 } from './shared.js';
 
-function Store(state) {
+function Store(state, options) {
 	this._observers = { pre: blankObject(), post: blankObject() };
 	this._changeHandlers = [];
 	this._dependents = [];
@@ -16,6 +17,7 @@ function Store(state) {
 	this._sortedComputedProperties = [];
 
 	this._state = assign({}, state);
+	this._differs = options && options.immutable ? differsImmutable : differs;
 }
 
 assign(Store.prototype, {
@@ -88,7 +90,7 @@ assign(Store.prototype, {
 
 				if (dirty) {
 					var newValue = fn.apply(null, values);
-					if (differs(newValue, value)) {
+					if (store._differs(newValue, value)) {
 						value = newValue;
 						changed[key] = true;
 						state[key] = value;
@@ -124,7 +126,7 @@ assign(Store.prototype, {
 
 		for (var key in newState) {
 			if (this._computed[key]) throw new Error("'" + key + "' is a read-only property");
-			if (differs(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 59cd2de125..72b12b5ef4 100644
--- a/test/js/samples/collapses-text-around-comments/expected-bundle.js
+++ b/test/js/samples/collapses-text-around-comments/expected-bundle.js
@@ -52,7 +52,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	return a !== b || ((a && 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) {
@@ -94,6 +94,7 @@ function init(component, options) {
 	component._observers = { pre: blankObject(), post: blankObject() };
 	component._handlers = blankObject();
 	component._bind = options._bind;
+	component._differs = differs;
 
 	component.options = options;
 	component.root = options.root || component;
@@ -151,7 +152,7 @@ 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;
 
diff --git a/test/js/samples/component-static-immutable/_config.js b/test/js/samples/component-static-immutable/_config.js
new file mode 100644
index 0000000000..06713941e0
--- /dev/null
+++ b/test/js/samples/component-static-immutable/_config.js
@@ -0,0 +1,5 @@
+export default {
+	options: {
+		immutable: true
+	}
+};
\ No newline at end of file
diff --git a/test/js/samples/component-static-immutable/expected-bundle.js b/test/js/samples/component-static-immutable/expected-bundle.js
new file mode 100644
index 0000000000..500322d902
--- /dev/null
+++ b/test/js/samples/component-static-immutable/expected-bundle.js
@@ -0,0 +1,238 @@
+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 differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+}
+
+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._differs = differs;
+
+	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 */
+var Nested = window.Nested;
+
+var immutable = true;
+
+function create_main_fragment(state, component) {
+
+	var nested = new Nested({
+		root: component.root,
+		data: { foo: "bar" }
+	});
+
+	return {
+		c: function create() {
+			nested._fragment.c();
+		},
+
+		m: function mount(target, anchor) {
+			nested._mount(target, anchor);
+		},
+
+		p: noop,
+
+		u: function unmount() {
+			nested._unmount();
+		},
+
+		d: function destroy$$1() {
+			nested.destroy(false);
+		}
+	};
+}
+
+function SvelteComponent(options) {
+	init(this, options);
+	if (options.immutable !== undefined ? options.immutable : immutable) {
+		this._differs = differsImmutable;
+	}
+	this._state = assign({}, options.data);
+
+	if (!options.root) {
+		this._oncreate = [];
+		this._beforecreate = [];
+		this._aftercreate = [];
+	}
+
+	this._fragment = create_main_fragment(this._state, this);
+
+	if (options.target) {
+		this._fragment.c();
+		this._fragment.m(options.target, options.anchor || null);
+
+		this._lock = true;
+		callAll(this._beforecreate);
+		callAll(this._oncreate);
+		callAll(this._aftercreate);
+		this._lock = false;
+	}
+}
+
+assign(SvelteComponent.prototype, proto);
+
+export default SvelteComponent;
diff --git a/test/js/samples/component-static-immutable/expected.js b/test/js/samples/component-static-immutable/expected.js
new file mode 100644
index 0000000000..811d5c50c4
--- /dev/null
+++ b/test/js/samples/component-static-immutable/expected.js
@@ -0,0 +1,64 @@
+/* generated by Svelte vX.Y.Z */
+import { assign, callAll, differsImmutable, init, noop, proto } from "svelte/shared.js";
+
+var Nested = window.Nested;
+
+var immutable = true;
+
+function create_main_fragment(state, component) {
+
+	var nested = new Nested({
+		root: component.root,
+		data: { foo: "bar" }
+	});
+
+	return {
+		c: function create() {
+			nested._fragment.c();
+		},
+
+		m: function mount(target, anchor) {
+			nested._mount(target, anchor);
+		},
+
+		p: noop,
+
+		u: function unmount() {
+			nested._unmount();
+		},
+
+		d: function destroy() {
+			nested.destroy(false);
+		}
+	};
+}
+
+function SvelteComponent(options) {
+	init(this, options);
+	if (options.immutable !== undefined ? options.immutable : immutable) {
+		this._differs = differsImmutable;
+	}
+	this._state = assign({}, options.data);
+
+	if (!options.root) {
+		this._oncreate = [];
+		this._beforecreate = [];
+		this._aftercreate = [];
+	}
+
+	this._fragment = create_main_fragment(this._state, this);
+
+	if (options.target) {
+		this._fragment.c();
+		this._fragment.m(options.target, options.anchor || null);
+
+		this._lock = true;
+		callAll(this._beforecreate);
+		callAll(this._oncreate);
+		callAll(this._aftercreate);
+		this._lock = false;
+	}
+}
+
+assign(SvelteComponent.prototype, proto);
+export default SvelteComponent;
\ No newline at end of file
diff --git a/test/js/samples/component-static-immutable/input.html b/test/js/samples/component-static-immutable/input.html
new file mode 100644
index 0000000000..df6c82ea81
--- /dev/null
+++ b/test/js/samples/component-static-immutable/input.html
@@ -0,0 +1,10 @@
+<Nested foo='bar'/>
+
+<script>
+	export default {
+		immutable: true,
+		components: {
+			Nested: window.Nested
+		}
+	};
+</script>
\ No newline at end of file
diff --git a/test/js/samples/component-static-immutable2/_config.js b/test/js/samples/component-static-immutable2/_config.js
new file mode 100644
index 0000000000..06713941e0
--- /dev/null
+++ b/test/js/samples/component-static-immutable2/_config.js
@@ -0,0 +1,5 @@
+export default {
+	options: {
+		immutable: true
+	}
+};
\ No newline at end of file
diff --git a/test/js/samples/component-static-immutable2/expected-bundle.js b/test/js/samples/component-static-immutable2/expected-bundle.js
new file mode 100644
index 0000000000..abab18060b
--- /dev/null
+++ b/test/js/samples/component-static-immutable2/expected-bundle.js
@@ -0,0 +1,236 @@
+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 differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+}
+
+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._differs = differs;
+
+	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 */
+var Nested = window.Nested;
+
+function create_main_fragment(state, component) {
+
+	var nested = new Nested({
+		root: component.root,
+		data: { foo: "bar" }
+	});
+
+	return {
+		c: function create() {
+			nested._fragment.c();
+		},
+
+		m: function mount(target, anchor) {
+			nested._mount(target, anchor);
+		},
+
+		p: noop,
+
+		u: function unmount() {
+			nested._unmount();
+		},
+
+		d: function destroy$$1() {
+			nested.destroy(false);
+		}
+	};
+}
+
+function SvelteComponent(options) {
+	init(this, options);
+	if (options.immutable !== undefined ? options.immutable : this.root.options.immutable) {
+		this._differs = differsImmutable;
+	}
+	this._state = assign({}, options.data);
+
+	if (!options.root) {
+		this._oncreate = [];
+		this._beforecreate = [];
+		this._aftercreate = [];
+	}
+
+	this._fragment = create_main_fragment(this._state, this);
+
+	if (options.target) {
+		this._fragment.c();
+		this._fragment.m(options.target, options.anchor || null);
+
+		this._lock = true;
+		callAll(this._beforecreate);
+		callAll(this._oncreate);
+		callAll(this._aftercreate);
+		this._lock = false;
+	}
+}
+
+assign(SvelteComponent.prototype, proto);
+
+export default SvelteComponent;
diff --git a/test/js/samples/component-static-immutable2/expected.js b/test/js/samples/component-static-immutable2/expected.js
new file mode 100644
index 0000000000..96dcb16874
--- /dev/null
+++ b/test/js/samples/component-static-immutable2/expected.js
@@ -0,0 +1,62 @@
+/* generated by Svelte vX.Y.Z */
+import { assign, callAll, differsImmutable, init, noop, proto } from "svelte/shared.js";
+
+var Nested = window.Nested;
+
+function create_main_fragment(state, component) {
+
+	var nested = new Nested({
+		root: component.root,
+		data: { foo: "bar" }
+	});
+
+	return {
+		c: function create() {
+			nested._fragment.c();
+		},
+
+		m: function mount(target, anchor) {
+			nested._mount(target, anchor);
+		},
+
+		p: noop,
+
+		u: function unmount() {
+			nested._unmount();
+		},
+
+		d: function destroy() {
+			nested.destroy(false);
+		}
+	};
+}
+
+function SvelteComponent(options) {
+	init(this, options);
+	if (options.immutable !== undefined ? options.immutable : this.root.options.immutable) {
+		this._differs = differsImmutable;
+	}
+	this._state = assign({}, options.data);
+
+	if (!options.root) {
+		this._oncreate = [];
+		this._beforecreate = [];
+		this._aftercreate = [];
+	}
+
+	this._fragment = create_main_fragment(this._state, this);
+
+	if (options.target) {
+		this._fragment.c();
+		this._fragment.m(options.target, options.anchor || null);
+
+		this._lock = true;
+		callAll(this._beforecreate);
+		callAll(this._oncreate);
+		callAll(this._aftercreate);
+		this._lock = false;
+	}
+}
+
+assign(SvelteComponent.prototype, proto);
+export default SvelteComponent;
\ No newline at end of file
diff --git a/test/js/samples/component-static-immutable2/input.html b/test/js/samples/component-static-immutable2/input.html
new file mode 100644
index 0000000000..44a2bf2bc1
--- /dev/null
+++ b/test/js/samples/component-static-immutable2/input.html
@@ -0,0 +1,9 @@
+<Nested foo='bar'/>
+
+<script>
+	export default {
+		components: {
+			Nested: window.Nested
+		}
+	};
+</script>
\ No newline at end of file
diff --git a/test/js/samples/component-static/expected-bundle.js b/test/js/samples/component-static/expected-bundle.js
index 708ef5be95..b89784944c 100644
--- a/test/js/samples/component-static/expected-bundle.js
+++ b/test/js/samples/component-static/expected-bundle.js
@@ -28,7 +28,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	return a !== b || ((a && 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) {
@@ -70,6 +70,7 @@ function init(component, options) {
 	component._observers = { pre: blankObject(), post: blankObject() };
 	component._handlers = blankObject();
 	component._bind = options._bind;
+	component._differs = differs;
 
 	component.options = options;
 	component.root = options.root || component;
@@ -127,7 +128,7 @@ 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;
 
diff --git a/test/js/samples/computed-collapsed-if/expected-bundle.js b/test/js/samples/computed-collapsed-if/expected-bundle.js
index b39f95a77b..b88fbb5e47 100644
--- a/test/js/samples/computed-collapsed-if/expected-bundle.js
+++ b/test/js/samples/computed-collapsed-if/expected-bundle.js
@@ -28,7 +28,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	return a !== b || ((a && 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) {
@@ -70,6 +70,7 @@ function init(component, options) {
 	component._observers = { pre: blankObject(), post: blankObject() };
 	component._handlers = blankObject();
 	component._bind = options._bind;
+	component._differs = differs;
 
 	component.options = options;
 	component.root = options.root || component;
@@ -127,7 +128,7 @@ 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;
 
@@ -209,8 +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..085365f4c5 100644
--- a/test/js/samples/computed-collapsed-if/expected.js
+++ b/test/js/samples/computed-collapsed-if/expected.js
@@ -1,5 +1,5 @@
 /* generated by Svelte vX.Y.Z */
-import { assign, differs, init, noop, proto } from "svelte/shared.js";
+import { assign, init, noop, proto } from "svelte/shared.js";
 
 function a(x) {
 	return x * 2;
@@ -41,8 +41,8 @@ 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 91662053a4..606b5dc9e8 100644
--- a/test/js/samples/css-media-query/expected-bundle.js
+++ b/test/js/samples/css-media-query/expected-bundle.js
@@ -48,7 +48,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	return a !== b || ((a && 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) {
@@ -90,6 +90,7 @@ function init(component, options) {
 	component._observers = { pre: blankObject(), post: blankObject() };
 	component._handlers = blankObject();
 	component._bind = options._bind;
+	component._differs = differs;
 
 	component.options = options;
 	component.root = options.root || component;
@@ -147,7 +148,7 @@ 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;
 
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 03e5cef1e2..0cc67aa9bc 100644
--- a/test/js/samples/css-shadow-dom-keyframes/expected-bundle.js
+++ b/test/js/samples/css-shadow-dom-keyframes/expected-bundle.js
@@ -40,7 +40,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	return a !== b || ((a && 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) {
@@ -82,6 +82,7 @@ function init(component, options) {
 	component._observers = { pre: blankObject(), post: blankObject() };
 	component._handlers = blankObject();
 	component._bind = options._bind;
+	component._differs = differs;
 
 	component.options = options;
 	component.root = options.root || component;
@@ -139,7 +140,7 @@ 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;
 
diff --git a/test/js/samples/deconflict-globals/expected-bundle.js b/test/js/samples/deconflict-globals/expected-bundle.js
index ba22542c4b..1a1e25de5a 100644
--- a/test/js/samples/deconflict-globals/expected-bundle.js
+++ b/test/js/samples/deconflict-globals/expected-bundle.js
@@ -28,7 +28,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	return a !== b || ((a && 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) {
@@ -70,6 +70,7 @@ function init(component, options) {
 	component._observers = { pre: blankObject(), post: blankObject() };
 	component._handlers = blankObject();
 	component._bind = options._bind;
+	component._differs = differs;
 
 	component.options = options;
 	component.root = options.root || component;
@@ -127,7 +128,7 @@ 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;
 
diff --git a/test/js/samples/do-use-dataset/expected-bundle.js b/test/js/samples/do-use-dataset/expected-bundle.js
index 2079e6607c..e3532c976a 100644
--- a/test/js/samples/do-use-dataset/expected-bundle.js
+++ b/test/js/samples/do-use-dataset/expected-bundle.js
@@ -44,7 +44,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	return a !== b || ((a && 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) {
@@ -86,6 +86,7 @@ function init(component, options) {
 	component._observers = { pre: blankObject(), post: blankObject() };
 	component._handlers = blankObject();
 	component._bind = options._bind;
+	component._differs = differs;
 
 	component.options = options;
 	component.root = options.root || component;
@@ -143,7 +144,7 @@ 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;
 
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 efcfcc8f30..df67cf01e8 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
@@ -48,7 +48,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	return a !== b || ((a && 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) {
@@ -90,6 +90,7 @@ function init(component, options) {
 	component._observers = { pre: blankObject(), post: blankObject() };
 	component._handlers = blankObject();
 	component._bind = options._bind;
+	component._differs = differs;
 
 	component.options = options;
 	component.root = options.root || component;
@@ -147,7 +148,7 @@ 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;
 
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 cf43bbd130..55fd993d32 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
@@ -48,7 +48,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	return a !== b || ((a && 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) {
@@ -90,6 +90,7 @@ function init(component, options) {
 	component._observers = { pre: blankObject(), post: blankObject() };
 	component._handlers = blankObject();
 	component._bind = options._bind;
+	component._differs = differs;
 
 	component.options = options;
 	component.root = options.root || component;
@@ -147,7 +148,7 @@ 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;
 
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 e35826e354..524789a51a 100644
--- a/test/js/samples/each-block-changed-check/expected-bundle.js
+++ b/test/js/samples/each-block-changed-check/expected-bundle.js
@@ -60,7 +60,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	return a !== b || ((a && 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) {
@@ -102,6 +102,7 @@ function init(component, options) {
 	component._observers = { pre: blankObject(), post: blankObject() };
 	component._handlers = blankObject();
 	component._bind = options._bind;
+	component._differs = differs;
 
 	component.options = options;
 	component.root = options.root || component;
@@ -159,7 +160,7 @@ 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;
 
diff --git a/test/js/samples/event-handlers-custom/expected-bundle.js b/test/js/samples/event-handlers-custom/expected-bundle.js
index 43db3035a3..860d249ee0 100644
--- a/test/js/samples/event-handlers-custom/expected-bundle.js
+++ b/test/js/samples/event-handlers-custom/expected-bundle.js
@@ -40,7 +40,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	return a !== b || ((a && 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) {
@@ -82,6 +82,7 @@ function init(component, options) {
 	component._observers = { pre: blankObject(), post: blankObject() };
 	component._handlers = blankObject();
 	component._bind = options._bind;
+	component._differs = differs;
 
 	component.options = options;
 	component.root = options.root || component;
@@ -139,7 +140,7 @@ 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;
 
diff --git a/test/js/samples/head-no-whitespace/expected-bundle.js b/test/js/samples/head-no-whitespace/expected-bundle.js
index 91f894bc30..96d3b06cc8 100644
--- a/test/js/samples/head-no-whitespace/expected-bundle.js
+++ b/test/js/samples/head-no-whitespace/expected-bundle.js
@@ -40,7 +40,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	return a !== b || ((a && 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) {
@@ -82,6 +82,7 @@ function init(component, options) {
 	component._observers = { pre: blankObject(), post: blankObject() };
 	component._handlers = blankObject();
 	component._bind = options._bind;
+	component._differs = differs;
 
 	component.options = options;
 	component.root = options.root || component;
@@ -139,7 +140,7 @@ 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;
 
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 b309a25e96..29e8a05a8b 100644
--- a/test/js/samples/if-block-no-update/expected-bundle.js
+++ b/test/js/samples/if-block-no-update/expected-bundle.js
@@ -44,7 +44,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	return a !== b || ((a && 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) {
@@ -86,6 +86,7 @@ function init(component, options) {
 	component._observers = { pre: blankObject(), post: blankObject() };
 	component._handlers = blankObject();
 	component._bind = options._bind;
+	component._differs = differs;
 
 	component.options = options;
 	component.root = options.root || component;
@@ -143,7 +144,7 @@ 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;
 
diff --git a/test/js/samples/if-block-simple/expected-bundle.js b/test/js/samples/if-block-simple/expected-bundle.js
index 5084639f4b..80a2a1475c 100644
--- a/test/js/samples/if-block-simple/expected-bundle.js
+++ b/test/js/samples/if-block-simple/expected-bundle.js
@@ -44,7 +44,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	return a !== b || ((a && 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) {
@@ -86,6 +86,7 @@ function init(component, options) {
 	component._observers = { pre: blankObject(), post: blankObject() };
 	component._handlers = blankObject();
 	component._bind = options._bind;
+	component._differs = differs;
 
 	component.options = options;
 	component.root = options.root || component;
@@ -143,7 +144,7 @@ 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;
 
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 753d61db71..4348f9367e 100644
--- a/test/js/samples/inline-style-optimized-multiple/expected-bundle.js
+++ b/test/js/samples/inline-style-optimized-multiple/expected-bundle.js
@@ -44,7 +44,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	return a !== b || ((a && 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) {
@@ -86,6 +86,7 @@ function init(component, options) {
 	component._observers = { pre: blankObject(), post: blankObject() };
 	component._handlers = blankObject();
 	component._bind = options._bind;
+	component._differs = differs;
 
 	component.options = options;
 	component.root = options.root || component;
@@ -143,7 +144,7 @@ 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;
 
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 cf360881b1..017dc960fc 100644
--- a/test/js/samples/inline-style-optimized-url/expected-bundle.js
+++ b/test/js/samples/inline-style-optimized-url/expected-bundle.js
@@ -44,7 +44,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	return a !== b || ((a && 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) {
@@ -86,6 +86,7 @@ function init(component, options) {
 	component._observers = { pre: blankObject(), post: blankObject() };
 	component._handlers = blankObject();
 	component._bind = options._bind;
+	component._differs = differs;
 
 	component.options = options;
 	component.root = options.root || component;
@@ -143,7 +144,7 @@ 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;
 
diff --git a/test/js/samples/inline-style-optimized/expected-bundle.js b/test/js/samples/inline-style-optimized/expected-bundle.js
index 38024df4ff..fc1ba783cc 100644
--- a/test/js/samples/inline-style-optimized/expected-bundle.js
+++ b/test/js/samples/inline-style-optimized/expected-bundle.js
@@ -44,7 +44,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	return a !== b || ((a && 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) {
@@ -86,6 +86,7 @@ function init(component, options) {
 	component._observers = { pre: blankObject(), post: blankObject() };
 	component._handlers = blankObject();
 	component._bind = options._bind;
+	component._differs = differs;
 
 	component.options = options;
 	component.root = options.root || component;
@@ -143,7 +144,7 @@ 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;
 
diff --git a/test/js/samples/inline-style-unoptimized/expected-bundle.js b/test/js/samples/inline-style-unoptimized/expected-bundle.js
index 320c733a43..3958d3862b 100644
--- a/test/js/samples/inline-style-unoptimized/expected-bundle.js
+++ b/test/js/samples/inline-style-unoptimized/expected-bundle.js
@@ -44,7 +44,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	return a !== b || ((a && 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) {
@@ -86,6 +86,7 @@ function init(component, options) {
 	component._observers = { pre: blankObject(), post: blankObject() };
 	component._handlers = blankObject();
 	component._bind = options._bind;
+	component._differs = differs;
 
 	component.options = options;
 	component.root = options.root || component;
@@ -143,7 +144,7 @@ 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;
 
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 eacaca85a6..dbed2a12c0 100644
--- a/test/js/samples/input-without-blowback-guard/expected-bundle.js
+++ b/test/js/samples/input-without-blowback-guard/expected-bundle.js
@@ -48,7 +48,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	return a !== b || ((a && 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) {
@@ -90,6 +90,7 @@ function init(component, options) {
 	component._observers = { pre: blankObject(), post: blankObject() };
 	component._handlers = blankObject();
 	component._bind = options._bind;
+	component._differs = differs;
 
 	component.options = options;
 	component.root = options.root || component;
@@ -147,7 +148,7 @@ 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;
 
diff --git a/test/js/samples/legacy-input-type/expected-bundle.js b/test/js/samples/legacy-input-type/expected-bundle.js
index 7b730f08d9..5b49b4995a 100644
--- a/test/js/samples/legacy-input-type/expected-bundle.js
+++ b/test/js/samples/legacy-input-type/expected-bundle.js
@@ -46,7 +46,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	return a !== b || ((a && 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) {
@@ -88,6 +88,7 @@ function init(component, options) {
 	component._observers = { pre: blankObject(), post: blankObject() };
 	component._handlers = blankObject();
 	component._bind = options._bind;
+	component._differs = differs;
 
 	component.options = options;
 	component.root = options.root || component;
@@ -145,7 +146,7 @@ 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;
 
diff --git a/test/js/samples/legacy-quote-class/expected-bundle.js b/test/js/samples/legacy-quote-class/expected-bundle.js
index 499a82c46e..db13a962c9 100644
--- a/test/js/samples/legacy-quote-class/expected-bundle.js
+++ b/test/js/samples/legacy-quote-class/expected-bundle.js
@@ -63,7 +63,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	return a !== b || ((a && 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) {
@@ -105,6 +105,7 @@ function init(component, options) {
 	component._observers = { pre: blankObject(), post: blankObject() };
 	component._handlers = blankObject();
 	component._bind = options._bind;
+	component._differs = differs;
 
 	component.options = options;
 	component.root = options.root || component;
@@ -162,7 +163,7 @@ 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;
 
diff --git a/test/js/samples/media-bindings/expected-bundle.js b/test/js/samples/media-bindings/expected-bundle.js
index bbd56d8123..230454d955 100644
--- a/test/js/samples/media-bindings/expected-bundle.js
+++ b/test/js/samples/media-bindings/expected-bundle.js
@@ -56,7 +56,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	return a !== b || ((a && 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) {
@@ -98,6 +98,7 @@ function init(component, options) {
 	component._observers = { pre: blankObject(), post: blankObject() };
 	component._handlers = blankObject();
 	component._bind = options._bind;
+	component._differs = differs;
 
 	component.options = options;
 	component.root = options.root || component;
@@ -155,7 +156,7 @@ 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;
 
diff --git a/test/js/samples/non-imported-component/expected-bundle.js b/test/js/samples/non-imported-component/expected-bundle.js
index f8e0722db7..b037ff3ad4 100644
--- a/test/js/samples/non-imported-component/expected-bundle.js
+++ b/test/js/samples/non-imported-component/expected-bundle.js
@@ -42,7 +42,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	return a !== b || ((a && 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) {
@@ -84,6 +84,7 @@ function init(component, options) {
 	component._observers = { pre: blankObject(), post: blankObject() };
 	component._handlers = blankObject();
 	component._bind = options._bind;
+	component._differs = differs;
 
 	component.options = options;
 	component.root = options.root || component;
@@ -141,7 +142,7 @@ 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;
 
diff --git a/test/js/samples/onrender-onteardown-rewritten/expected-bundle.js b/test/js/samples/onrender-onteardown-rewritten/expected-bundle.js
index e53dd0de5e..c0d41a7c76 100644
--- a/test/js/samples/onrender-onteardown-rewritten/expected-bundle.js
+++ b/test/js/samples/onrender-onteardown-rewritten/expected-bundle.js
@@ -28,7 +28,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	return a !== b || ((a && 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) {
@@ -70,6 +70,7 @@ function init(component, options) {
 	component._observers = { pre: blankObject(), post: blankObject() };
 	component._handlers = blankObject();
 	component._bind = options._bind;
+	component._differs = differs;
 
 	component.options = options;
 	component.root = options.root || component;
@@ -127,7 +128,7 @@ 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;
 
diff --git a/test/js/samples/setup-method/expected-bundle.js b/test/js/samples/setup-method/expected-bundle.js
index 58ee3a67a0..d1b04e43a5 100644
--- a/test/js/samples/setup-method/expected-bundle.js
+++ b/test/js/samples/setup-method/expected-bundle.js
@@ -28,7 +28,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	return a !== b || ((a && 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) {
@@ -70,6 +70,7 @@ function init(component, options) {
 	component._observers = { pre: blankObject(), post: blankObject() };
 	component._handlers = blankObject();
 	component._bind = options._bind;
+	component._differs = differs;
 
 	component.options = options;
 	component.root = options.root || component;
@@ -127,7 +128,7 @@ 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;
 
diff --git a/test/js/samples/svg-title/expected-bundle.js b/test/js/samples/svg-title/expected-bundle.js
index 12f06bcf92..21f8467d3b 100644
--- a/test/js/samples/svg-title/expected-bundle.js
+++ b/test/js/samples/svg-title/expected-bundle.js
@@ -48,7 +48,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	return a !== b || ((a && 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) {
@@ -90,6 +90,7 @@ function init(component, options) {
 	component._observers = { pre: blankObject(), post: blankObject() };
 	component._handlers = blankObject();
 	component._bind = options._bind;
+	component._differs = differs;
 
 	component.options = options;
 	component.root = options.root || component;
@@ -147,7 +148,7 @@ 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;
 
diff --git a/test/js/samples/title/expected-bundle.js b/test/js/samples/title/expected-bundle.js
index 6eb3471b5b..bebf5e4466 100644
--- a/test/js/samples/title/expected-bundle.js
+++ b/test/js/samples/title/expected-bundle.js
@@ -28,7 +28,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	return a !== b || ((a && 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) {
@@ -70,6 +70,7 @@ function init(component, options) {
 	component._observers = { pre: blankObject(), post: blankObject() };
 	component._handlers = blankObject();
 	component._bind = options._bind;
+	component._differs = differs;
 
 	component.options = options;
 	component.root = options.root || component;
@@ -127,7 +128,7 @@ 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;
 
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 e2ee1e61fb..f7302d8bd7 100644
--- a/test/js/samples/use-elements-as-anchors/expected-bundle.js
+++ b/test/js/samples/use-elements-as-anchors/expected-bundle.js
@@ -52,7 +52,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	return a !== b || ((a && 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) {
@@ -94,6 +94,7 @@ function init(component, options) {
 	component._observers = { pre: blankObject(), post: blankObject() };
 	component._handlers = blankObject();
 	component._bind = options._bind;
+	component._differs = differs;
 
 	component.options = options;
 	component.root = options.root || component;
@@ -151,7 +152,7 @@ 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;
 
diff --git a/test/js/samples/window-binding-scroll/expected-bundle.js b/test/js/samples/window-binding-scroll/expected-bundle.js
index a8a932c8b7..f522e5f96d 100644
--- a/test/js/samples/window-binding-scroll/expected-bundle.js
+++ b/test/js/samples/window-binding-scroll/expected-bundle.js
@@ -48,7 +48,7 @@ function destroy(detach) {
 }
 
 function differs(a, b) {
-	return a !== b || ((a && 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) {
@@ -90,6 +90,7 @@ function init(component, options) {
 	component._observers = { pre: blankObject(), post: blankObject() };
 	component._handlers = blankObject();
 	component._bind = options._bind;
+	component._differs = differs;
 
 	component.options = options;
 	component.root = options.root || component;
@@ -147,7 +148,7 @@ 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;
 
diff --git a/test/runtime/index.js b/test/runtime/index.js
index 778f47c0cc..8ec4c5194a 100644
--- a/test/runtime/index.js
+++ b/test/runtime/index.js
@@ -66,6 +66,7 @@ describe("runtime", () => {
 			compileOptions.hydratable = hydrate;
 			compileOptions.dev = config.dev;
 			compileOptions.store = !!config.store;
+			compileOptions.immutable = config.immutable;
 
 			// check that no ES2015+ syntax slipped in
 			if (!config.allowES2015) {
@@ -160,7 +161,8 @@ describe("runtime", () => {
 						target,
 						hydrate,
 						data: config.data,
-						store: (config.store !== true && config.store)
+						store: (config.store !== true && config.store),
+						immutable: config.immutable
 					}, config.options || {});
 
 					const component = new SvelteComponent(options);
diff --git a/test/runtime/samples/immutable-mutable/Nested.html b/test/runtime/samples/immutable-mutable/Nested.html
new file mode 100644
index 0000000000..02278e385e
--- /dev/null
+++ b/test/runtime/samples/immutable-mutable/Nested.html
@@ -0,0 +1,13 @@
+<h3>Called {{count}} times.</h3>
+
+<script>
+  export default {
+    immutable: false,
+    data() {
+      return {
+        count: 0,
+        foo: { bar: 'baz' }
+      };
+    }
+  }
+</script>
\ No newline at end of file
diff --git a/test/runtime/samples/immutable-mutable/_config.js b/test/runtime/samples/immutable-mutable/_config.js
new file mode 100644
index 0000000000..5dab0f239b
--- /dev/null
+++ b/test/runtime/samples/immutable-mutable/_config.js
@@ -0,0 +1,16 @@
+export default {
+	immutable: true,
+	html: `<div><h3>Called 0 times.</h3></div>`,
+
+	test(assert, component, target, window) {
+		var nested = component.refs.nested;
+		nested.observe('foo', foo => {
+			nested.set({ count: nested.get('count') + 1 });
+		});
+
+		assert.htmlEqual(target.innerHTML, `<div><h3>Called 1 times.</h3></div>`);
+
+		nested.set({ foo: nested.get('foo') });
+		assert.htmlEqual(target.innerHTML, `<div><h3>Called 2 times.</h3></div>`);
+	}
+};
diff --git a/test/runtime/samples/immutable-mutable/main.html b/test/runtime/samples/immutable-mutable/main.html
new file mode 100644
index 0000000000..4e36143361
--- /dev/null
+++ b/test/runtime/samples/immutable-mutable/main.html
@@ -0,0 +1,13 @@
+<div>
+  <Nested ref:nested />
+</div>
+
+<script>
+	import Nested from './Nested.html';
+
+	export default {
+		components: {
+			Nested
+		}
+	};
+</script>
diff --git a/test/runtime/samples/immutable-nested/Nested.html b/test/runtime/samples/immutable-nested/Nested.html
new file mode 100644
index 0000000000..05eb9f3fdf
--- /dev/null
+++ b/test/runtime/samples/immutable-nested/Nested.html
@@ -0,0 +1,12 @@
+<h3>Called {{count}} times.</h3>
+
+<script>
+	export default {
+		data() {
+			return {
+				count: 0,
+				foo: { bar: 'baz' }
+			};
+		}
+	}
+</script>
\ No newline at end of file
diff --git a/test/runtime/samples/immutable-nested/_config.js b/test/runtime/samples/immutable-nested/_config.js
new file mode 100644
index 0000000000..541566ce4d
--- /dev/null
+++ b/test/runtime/samples/immutable-nested/_config.js
@@ -0,0 +1,16 @@
+export default {
+	immutable: true,
+	html: `<div><h3>Called 0 times.</h3></div>`,
+
+	test(assert, component, target, window) {
+		var nested = component.refs.nested;
+		nested.observe('foo', foo => {
+			nested.set({ count: nested.get('count') + 1 });
+		});
+
+		assert.htmlEqual(target.innerHTML, `<div><h3>Called 1 times.</h3></div>`);
+
+		nested.set({ foo: nested.get('foo') });
+		assert.htmlEqual(target.innerHTML, `<div><h3>Called 1 times.</h3></div>`);
+	}
+};
diff --git a/test/runtime/samples/immutable-nested/main.html b/test/runtime/samples/immutable-nested/main.html
new file mode 100644
index 0000000000..4e36143361
--- /dev/null
+++ b/test/runtime/samples/immutable-nested/main.html
@@ -0,0 +1,13 @@
+<div>
+  <Nested ref:nested />
+</div>
+
+<script>
+	import Nested from './Nested.html';
+
+	export default {
+		components: {
+			Nested
+		}
+	};
+</script>
diff --git a/test/runtime/samples/immutable-root/_config.js b/test/runtime/samples/immutable-root/_config.js
new file mode 100644
index 0000000000..a862008d7d
--- /dev/null
+++ b/test/runtime/samples/immutable-root/_config.js
@@ -0,0 +1,15 @@
+export default {
+	immutable: true,
+	html: `<div><h3>Called 0 times.</h3></div>`,
+
+	test(assert, component, target, window) {
+		component.observe('foo', foo => {
+			component.set({ count: component.get('count') + 1 });
+		});
+
+		assert.htmlEqual(target.innerHTML, `<div><h3>Called 1 times.</h3></div>`);
+
+		component.set({ foo: component.get('foo') });
+		assert.htmlEqual(target.innerHTML, `<div><h3>Called 1 times.</h3></div>`);
+	}
+};
diff --git a/test/runtime/samples/immutable-root/main.html b/test/runtime/samples/immutable-root/main.html
new file mode 100644
index 0000000000..087f561caf
--- /dev/null
+++ b/test/runtime/samples/immutable-root/main.html
@@ -0,0 +1,14 @@
+<div>
+	<h3>Called {{count}} times.</h3>
+</div>
+
+<script>
+  export default {
+		data() {
+			return {
+				count: 0,
+				foo: { bar: 'baz' }
+			};
+		}
+  }
+</script>
\ No newline at end of file
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);
+		});
+	});
 });