diff --git a/src/generators/dom/index.ts b/src/generators/dom/index.ts
index 2f88185fff..1d25c4bcfc 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;`;
 
@@ -174,7 +174,7 @@ export default function dom(
 		? `@proto`
 		: deindent`
 		{
-			${['destroy', 'get', 'fire', 'observe', 'on', 'set', 'teardown', '_set', '_mount', '_unmount']
+			${['destroy', 'get', 'fire', 'observe', 'on', 'set', 'teardown', '_set', '_mount', '_unmount', '_differs']
 				.map(n => `${n}: @${n === 'teardown' ? 'destroy' : n}`)
 				.join(',\n')}
 		}`;
@@ -360,6 +360,8 @@ export default function dom(
 		`);
 	}
 
+	const immutable = templateProperties.immutable ? templateProperties.immutable.value.value : options.immutable;
+
 	builder.addBlock(deindent`
 		${options.dev && deindent`
 			${name}.prototype._checkReadOnly = function _checkReadOnly(newState) {
@@ -379,6 +381,8 @@ export default function dom(
 		${templateProperties.setup && `%setup(${name});`}
 
 		${templateProperties.preload && `${name}.preload = %preload;`}
+
+		${immutable && `${name}.prototype._differs = @_differsImmutable;`}
 	`);
 
 	const usedHelpers = new Set();
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..cf953e4bf1 100644
--- a/src/shared/index.js
+++ b/src/shared/index.js
@@ -25,8 +25,12 @@ export function destroyDev(detach) {
 	};
 }
 
-export function differs(a, b) {
-	return a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+export function _differs(a, b) {
+	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) {
@@ -150,7 +154,7 @@ 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;
 
@@ -211,7 +215,8 @@ export var proto = {
 	_recompute: noop,
 	_set: _set,
 	_mount: _mount,
-	_unmount: _unmount
+	_unmount: _unmount,
+	_differs: _differs
 };
 
 export var protoDev = {
@@ -225,5 +230,6 @@ export var protoDev = {
 	_recompute: noop,
 	_set: _set,
 	_mount: _mount,
-	_unmount: _unmount
+	_unmount: _unmount,
+	_differs: _differs
 };
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..63a99cca05 100644
--- a/store.js
+++ b/store.js
@@ -1,13 +1,14 @@
 import {
 	assign,
 	blankObject,
-	differs,
+	_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 33854eb0e6..8520eae5a7 100644
--- a/test/js/samples/collapses-text-around-comments/expected-bundle.js
+++ b/test/js/samples/collapses-text-around-comments/expected-bundle.js
@@ -51,8 +51,8 @@ function destroy(detach) {
 	this._fragment = this._state = null;
 }
 
-function differs(a, b) {
-	return a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+function _differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -151,7 +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;
 
@@ -189,7 +189,8 @@ var proto = {
 	_recompute: noop,
 	_set: _set,
 	_mount: _mount,
-	_unmount: _unmount
+	_unmount: _unmount,
+	_differs: _differs
 };
 
 /* generated by Svelte vX.Y.Z */
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..18ca967e92
--- /dev/null
+++ b/test/js/samples/component-static-immutable/expected-bundle.js
@@ -0,0 +1,235 @@
+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.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,
+	_differs: _differs
+};
+
+/* 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);
+	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);
+
+SvelteComponent.prototype._differs = _differsImmutable;
+
+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..028dc9e64c
--- /dev/null
+++ b/test/js/samples/component-static-immutable/expected.js
@@ -0,0 +1,61 @@
+/* generated by Svelte vX.Y.Z */
+import { _differsImmutable, assign, callAll, 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);
+	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);
+
+SvelteComponent.prototype._differs = _differsImmutable;
+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..18ca967e92
--- /dev/null
+++ b/test/js/samples/component-static-immutable2/expected-bundle.js
@@ -0,0 +1,235 @@
+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.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,
+	_differs: _differs
+};
+
+/* 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);
+	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);
+
+SvelteComponent.prototype._differs = _differsImmutable;
+
+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..028dc9e64c
--- /dev/null
+++ b/test/js/samples/component-static-immutable2/expected.js
@@ -0,0 +1,61 @@
+/* generated by Svelte vX.Y.Z */
+import { _differsImmutable, assign, callAll, 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);
+	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);
+
+SvelteComponent.prototype._differs = _differsImmutable;
+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 5047d48b5e..3db3d982e1 100644
--- a/test/js/samples/component-static/expected-bundle.js
+++ b/test/js/samples/component-static/expected-bundle.js
@@ -27,8 +27,8 @@ function destroy(detach) {
 	this._fragment = this._state = null;
 }
 
-function differs(a, b) {
-	return a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+function _differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -127,7 +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;
 
@@ -165,7 +165,8 @@ var proto = {
 	_recompute: noop,
 	_set: _set,
 	_mount: _mount,
-	_unmount: _unmount
+	_unmount: _unmount,
+	_differs: _differs
 };
 
 /* generated by Svelte vX.Y.Z */
diff --git a/test/js/samples/computed-collapsed-if/expected-bundle.js b/test/js/samples/computed-collapsed-if/expected-bundle.js
index 64b09b4353..97faae3978 100644
--- a/test/js/samples/computed-collapsed-if/expected-bundle.js
+++ b/test/js/samples/computed-collapsed-if/expected-bundle.js
@@ -27,8 +27,8 @@ function destroy(detach) {
 	this._fragment = this._state = null;
 }
 
-function differs(a, b) {
-	return a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+function _differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -127,7 +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;
 
@@ -165,7 +165,8 @@ var proto = {
 	_recompute: noop,
 	_set: _set,
 	_mount: _mount,
-	_unmount: _unmount
+	_unmount: _unmount,
+	_differs: _differs
 };
 
 /* generated by Svelte vX.Y.Z */
@@ -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 e4a2fe00ef..d87ef16f92 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 66bb102184..fb4f540eea 100644
--- a/test/js/samples/css-media-query/expected-bundle.js
+++ b/test/js/samples/css-media-query/expected-bundle.js
@@ -47,8 +47,8 @@ function destroy(detach) {
 	this._fragment = this._state = null;
 }
 
-function differs(a, b) {
-	return a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+function _differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -147,7 +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;
 
@@ -185,7 +185,8 @@ var proto = {
 	_recompute: noop,
 	_set: _set,
 	_mount: _mount,
-	_unmount: _unmount
+	_unmount: _unmount,
+	_differs: _differs
 };
 
 /* generated by Svelte vX.Y.Z */
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 486c2d1d82..6017c3a0d7 100644
--- a/test/js/samples/css-shadow-dom-keyframes/expected-bundle.js
+++ b/test/js/samples/css-shadow-dom-keyframes/expected-bundle.js
@@ -39,8 +39,8 @@ function destroy(detach) {
 	this._fragment = this._state = null;
 }
 
-function differs(a, b) {
-	return a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+function _differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -139,7 +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;
 
@@ -177,7 +177,8 @@ var proto = {
 	_recompute: noop,
 	_set: _set,
 	_mount: _mount,
-	_unmount: _unmount
+	_unmount: _unmount,
+	_differs: _differs
 };
 
 /* generated by Svelte vX.Y.Z */
diff --git a/test/js/samples/deconflict-globals/expected-bundle.js b/test/js/samples/deconflict-globals/expected-bundle.js
index 841aaf7111..2d75a472bd 100644
--- a/test/js/samples/deconflict-globals/expected-bundle.js
+++ b/test/js/samples/deconflict-globals/expected-bundle.js
@@ -27,8 +27,8 @@ function destroy(detach) {
 	this._fragment = this._state = null;
 }
 
-function differs(a, b) {
-	return a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+function _differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -127,7 +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;
 
@@ -165,7 +165,8 @@ var proto = {
 	_recompute: noop,
 	_set: _set,
 	_mount: _mount,
-	_unmount: _unmount
+	_unmount: _unmount,
+	_differs: _differs
 };
 
 /* generated by Svelte vX.Y.Z */
diff --git a/test/js/samples/do-use-dataset/expected-bundle.js b/test/js/samples/do-use-dataset/expected-bundle.js
index b6667c9c91..2482e65cbf 100644
--- a/test/js/samples/do-use-dataset/expected-bundle.js
+++ b/test/js/samples/do-use-dataset/expected-bundle.js
@@ -43,8 +43,8 @@ function destroy(detach) {
 	this._fragment = this._state = null;
 }
 
-function differs(a, b) {
-	return a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+function _differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -143,7 +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;
 
@@ -181,7 +181,8 @@ var proto = {
 	_recompute: noop,
 	_set: _set,
 	_mount: _mount,
-	_unmount: _unmount
+	_unmount: _unmount,
+	_differs: _differs
 };
 
 /* generated by Svelte vX.Y.Z */
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 643e302968..9efc43320f 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
@@ -47,8 +47,8 @@ function destroy(detach) {
 	this._fragment = this._state = null;
 }
 
-function differs(a, b) {
-	return a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+function _differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -147,7 +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;
 
@@ -185,7 +185,8 @@ var proto = {
 	_recompute: noop,
 	_set: _set,
 	_mount: _mount,
-	_unmount: _unmount
+	_unmount: _unmount,
+	_differs: _differs
 };
 
 /* generated by Svelte vX.Y.Z */
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 5c9ef31f54..2a6a930ea1 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
@@ -47,8 +47,8 @@ function destroy(detach) {
 	this._fragment = this._state = null;
 }
 
-function differs(a, b) {
-	return a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+function _differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -147,7 +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;
 
@@ -185,7 +185,8 @@ var proto = {
 	_recompute: noop,
 	_set: _set,
 	_mount: _mount,
-	_unmount: _unmount
+	_unmount: _unmount,
+	_differs: _differs
 };
 
 /* generated by Svelte vX.Y.Z */
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 cc8a394ac1..626c47980b 100644
--- a/test/js/samples/each-block-changed-check/expected-bundle.js
+++ b/test/js/samples/each-block-changed-check/expected-bundle.js
@@ -59,8 +59,8 @@ function destroy(detach) {
 	this._fragment = this._state = null;
 }
 
-function differs(a, b) {
-	return a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+function _differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -159,7 +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;
 
@@ -197,7 +197,8 @@ var proto = {
 	_recompute: noop,
 	_set: _set,
 	_mount: _mount,
-	_unmount: _unmount
+	_unmount: _unmount,
+	_differs: _differs
 };
 
 /* generated by Svelte vX.Y.Z */
diff --git a/test/js/samples/event-handlers-custom/expected-bundle.js b/test/js/samples/event-handlers-custom/expected-bundle.js
index 252257d9e2..4be9a16f0b 100644
--- a/test/js/samples/event-handlers-custom/expected-bundle.js
+++ b/test/js/samples/event-handlers-custom/expected-bundle.js
@@ -39,8 +39,8 @@ function destroy(detach) {
 	this._fragment = this._state = null;
 }
 
-function differs(a, b) {
-	return a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+function _differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -139,7 +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;
 
@@ -177,7 +177,8 @@ var proto = {
 	_recompute: noop,
 	_set: _set,
 	_mount: _mount,
-	_unmount: _unmount
+	_unmount: _unmount,
+	_differs: _differs
 };
 
 /* generated by Svelte vX.Y.Z */
diff --git a/test/js/samples/head-no-whitespace/expected-bundle.js b/test/js/samples/head-no-whitespace/expected-bundle.js
index 60a9e85bf0..a50f2dbef5 100644
--- a/test/js/samples/head-no-whitespace/expected-bundle.js
+++ b/test/js/samples/head-no-whitespace/expected-bundle.js
@@ -39,8 +39,8 @@ function destroy(detach) {
 	this._fragment = this._state = null;
 }
 
-function differs(a, b) {
-	return a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+function _differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -139,7 +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;
 
@@ -177,7 +177,8 @@ var proto = {
 	_recompute: noop,
 	_set: _set,
 	_mount: _mount,
-	_unmount: _unmount
+	_unmount: _unmount,
+	_differs: _differs
 };
 
 /* generated by Svelte vX.Y.Z */
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 6caf1e5853..2e6975d978 100644
--- a/test/js/samples/if-block-no-update/expected-bundle.js
+++ b/test/js/samples/if-block-no-update/expected-bundle.js
@@ -43,8 +43,8 @@ function destroy(detach) {
 	this._fragment = this._state = null;
 }
 
-function differs(a, b) {
-	return a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+function _differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -143,7 +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;
 
@@ -181,7 +181,8 @@ var proto = {
 	_recompute: noop,
 	_set: _set,
 	_mount: _mount,
-	_unmount: _unmount
+	_unmount: _unmount,
+	_differs: _differs
 };
 
 /* generated by Svelte vX.Y.Z */
diff --git a/test/js/samples/if-block-simple/expected-bundle.js b/test/js/samples/if-block-simple/expected-bundle.js
index 78b31ecb3d..d18967e282 100644
--- a/test/js/samples/if-block-simple/expected-bundle.js
+++ b/test/js/samples/if-block-simple/expected-bundle.js
@@ -43,8 +43,8 @@ function destroy(detach) {
 	this._fragment = this._state = null;
 }
 
-function differs(a, b) {
-	return a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+function _differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -143,7 +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;
 
@@ -181,7 +181,8 @@ var proto = {
 	_recompute: noop,
 	_set: _set,
 	_mount: _mount,
-	_unmount: _unmount
+	_unmount: _unmount,
+	_differs: _differs
 };
 
 /* generated by Svelte vX.Y.Z */
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 b40b46e4c5..987b425333 100644
--- a/test/js/samples/inline-style-optimized-multiple/expected-bundle.js
+++ b/test/js/samples/inline-style-optimized-multiple/expected-bundle.js
@@ -43,8 +43,8 @@ function destroy(detach) {
 	this._fragment = this._state = null;
 }
 
-function differs(a, b) {
-	return a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+function _differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -143,7 +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;
 
@@ -181,7 +181,8 @@ var proto = {
 	_recompute: noop,
 	_set: _set,
 	_mount: _mount,
-	_unmount: _unmount
+	_unmount: _unmount,
+	_differs: _differs
 };
 
 /* generated by Svelte vX.Y.Z */
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 ce83c0473c..79117c831e 100644
--- a/test/js/samples/inline-style-optimized-url/expected-bundle.js
+++ b/test/js/samples/inline-style-optimized-url/expected-bundle.js
@@ -43,8 +43,8 @@ function destroy(detach) {
 	this._fragment = this._state = null;
 }
 
-function differs(a, b) {
-	return a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+function _differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -143,7 +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;
 
@@ -181,7 +181,8 @@ var proto = {
 	_recompute: noop,
 	_set: _set,
 	_mount: _mount,
-	_unmount: _unmount
+	_unmount: _unmount,
+	_differs: _differs
 };
 
 /* generated by Svelte vX.Y.Z */
diff --git a/test/js/samples/inline-style-optimized/expected-bundle.js b/test/js/samples/inline-style-optimized/expected-bundle.js
index 60d3574d4f..ff75016f84 100644
--- a/test/js/samples/inline-style-optimized/expected-bundle.js
+++ b/test/js/samples/inline-style-optimized/expected-bundle.js
@@ -43,8 +43,8 @@ function destroy(detach) {
 	this._fragment = this._state = null;
 }
 
-function differs(a, b) {
-	return a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+function _differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -143,7 +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;
 
@@ -181,7 +181,8 @@ var proto = {
 	_recompute: noop,
 	_set: _set,
 	_mount: _mount,
-	_unmount: _unmount
+	_unmount: _unmount,
+	_differs: _differs
 };
 
 /* generated by Svelte vX.Y.Z */
diff --git a/test/js/samples/inline-style-unoptimized/expected-bundle.js b/test/js/samples/inline-style-unoptimized/expected-bundle.js
index 368d9aeb15..903af075b8 100644
--- a/test/js/samples/inline-style-unoptimized/expected-bundle.js
+++ b/test/js/samples/inline-style-unoptimized/expected-bundle.js
@@ -43,8 +43,8 @@ function destroy(detach) {
 	this._fragment = this._state = null;
 }
 
-function differs(a, b) {
-	return a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+function _differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -143,7 +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;
 
@@ -181,7 +181,8 @@ var proto = {
 	_recompute: noop,
 	_set: _set,
 	_mount: _mount,
-	_unmount: _unmount
+	_unmount: _unmount,
+	_differs: _differs
 };
 
 /* generated by Svelte vX.Y.Z */
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 dcb3d2e061..a0f57143e2 100644
--- a/test/js/samples/input-without-blowback-guard/expected-bundle.js
+++ b/test/js/samples/input-without-blowback-guard/expected-bundle.js
@@ -47,8 +47,8 @@ function destroy(detach) {
 	this._fragment = this._state = null;
 }
 
-function differs(a, b) {
-	return a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+function _differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -147,7 +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;
 
@@ -185,7 +185,8 @@ var proto = {
 	_recompute: noop,
 	_set: _set,
 	_mount: _mount,
-	_unmount: _unmount
+	_unmount: _unmount,
+	_differs: _differs
 };
 
 /* generated by Svelte vX.Y.Z */
diff --git a/test/js/samples/legacy-input-type/expected-bundle.js b/test/js/samples/legacy-input-type/expected-bundle.js
index b0174e2105..d08fda0519 100644
--- a/test/js/samples/legacy-input-type/expected-bundle.js
+++ b/test/js/samples/legacy-input-type/expected-bundle.js
@@ -45,8 +45,8 @@ function destroy(detach) {
 	this._fragment = this._state = null;
 }
 
-function differs(a, b) {
-	return a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+function _differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -145,7 +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;
 
@@ -183,7 +183,8 @@ var proto = {
 	_recompute: noop,
 	_set: _set,
 	_mount: _mount,
-	_unmount: _unmount
+	_unmount: _unmount,
+	_differs: _differs
 };
 
 /* generated by Svelte vX.Y.Z */
diff --git a/test/js/samples/legacy-quote-class/expected-bundle.js b/test/js/samples/legacy-quote-class/expected-bundle.js
index 3956acd874..79a5921c4d 100644
--- a/test/js/samples/legacy-quote-class/expected-bundle.js
+++ b/test/js/samples/legacy-quote-class/expected-bundle.js
@@ -62,8 +62,8 @@ function destroy(detach) {
 	this._fragment = this._state = null;
 }
 
-function differs(a, b) {
-	return a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+function _differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -162,7 +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;
 
@@ -200,7 +200,8 @@ var proto = {
 	_recompute: noop,
 	_set: _set,
 	_mount: _mount,
-	_unmount: _unmount
+	_unmount: _unmount,
+	_differs: _differs
 };
 
 /* generated by Svelte vX.Y.Z */
diff --git a/test/js/samples/media-bindings/expected-bundle.js b/test/js/samples/media-bindings/expected-bundle.js
index 75e852e835..9427fbe0a4 100644
--- a/test/js/samples/media-bindings/expected-bundle.js
+++ b/test/js/samples/media-bindings/expected-bundle.js
@@ -55,8 +55,8 @@ function destroy(detach) {
 	this._fragment = this._state = null;
 }
 
-function differs(a, b) {
-	return a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+function _differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -155,7 +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;
 
@@ -193,7 +193,8 @@ var proto = {
 	_recompute: noop,
 	_set: _set,
 	_mount: _mount,
-	_unmount: _unmount
+	_unmount: _unmount,
+	_differs: _differs
 };
 
 /* generated by Svelte vX.Y.Z */
diff --git a/test/js/samples/non-imported-component/expected-bundle.js b/test/js/samples/non-imported-component/expected-bundle.js
index 1b85f2f9d9..2026d476ed 100644
--- a/test/js/samples/non-imported-component/expected-bundle.js
+++ b/test/js/samples/non-imported-component/expected-bundle.js
@@ -41,8 +41,8 @@ function destroy(detach) {
 	this._fragment = this._state = null;
 }
 
-function differs(a, b) {
-	return a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+function _differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -141,7 +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;
 
@@ -179,7 +179,8 @@ var proto = {
 	_recompute: noop,
 	_set: _set,
 	_mount: _mount,
-	_unmount: _unmount
+	_unmount: _unmount,
+	_differs: _differs
 };
 
 /* generated by Svelte vX.Y.Z */
diff --git a/test/js/samples/onrender-onteardown-rewritten/expected-bundle.js b/test/js/samples/onrender-onteardown-rewritten/expected-bundle.js
index 9f59cc8a9a..e77cc220bf 100644
--- a/test/js/samples/onrender-onteardown-rewritten/expected-bundle.js
+++ b/test/js/samples/onrender-onteardown-rewritten/expected-bundle.js
@@ -27,8 +27,8 @@ function destroy(detach) {
 	this._fragment = this._state = null;
 }
 
-function differs(a, b) {
-	return a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+function _differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -127,7 +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;
 
@@ -165,7 +165,8 @@ var proto = {
 	_recompute: noop,
 	_set: _set,
 	_mount: _mount,
-	_unmount: _unmount
+	_unmount: _unmount,
+	_differs: _differs
 };
 
 /* generated by Svelte vX.Y.Z */
diff --git a/test/js/samples/setup-method/expected-bundle.js b/test/js/samples/setup-method/expected-bundle.js
index 988103bc32..530a65fb1e 100644
--- a/test/js/samples/setup-method/expected-bundle.js
+++ b/test/js/samples/setup-method/expected-bundle.js
@@ -27,8 +27,8 @@ function destroy(detach) {
 	this._fragment = this._state = null;
 }
 
-function differs(a, b) {
-	return a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+function _differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -127,7 +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;
 
@@ -165,7 +165,8 @@ var proto = {
 	_recompute: noop,
 	_set: _set,
 	_mount: _mount,
-	_unmount: _unmount
+	_unmount: _unmount,
+	_differs: _differs
 };
 
 /* generated by Svelte vX.Y.Z */
diff --git a/test/js/samples/svg-title/expected-bundle.js b/test/js/samples/svg-title/expected-bundle.js
index 2ded30910d..2cb1bf8ca9 100644
--- a/test/js/samples/svg-title/expected-bundle.js
+++ b/test/js/samples/svg-title/expected-bundle.js
@@ -47,8 +47,8 @@ function destroy(detach) {
 	this._fragment = this._state = null;
 }
 
-function differs(a, b) {
-	return a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+function _differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -147,7 +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;
 
@@ -185,7 +185,8 @@ var proto = {
 	_recompute: noop,
 	_set: _set,
 	_mount: _mount,
-	_unmount: _unmount
+	_unmount: _unmount,
+	_differs: _differs
 };
 
 /* generated by Svelte vX.Y.Z */
diff --git a/test/js/samples/title/expected-bundle.js b/test/js/samples/title/expected-bundle.js
index f52f89a71a..36b72b2e93 100644
--- a/test/js/samples/title/expected-bundle.js
+++ b/test/js/samples/title/expected-bundle.js
@@ -27,8 +27,8 @@ function destroy(detach) {
 	this._fragment = this._state = null;
 }
 
-function differs(a, b) {
-	return a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+function _differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -127,7 +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;
 
@@ -165,7 +165,8 @@ var proto = {
 	_recompute: noop,
 	_set: _set,
 	_mount: _mount,
-	_unmount: _unmount
+	_unmount: _unmount,
+	_differs: _differs
 };
 
 /* generated by Svelte vX.Y.Z */
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 6ece6bffa7..e08d4d3831 100644
--- a/test/js/samples/use-elements-as-anchors/expected-bundle.js
+++ b/test/js/samples/use-elements-as-anchors/expected-bundle.js
@@ -51,8 +51,8 @@ function destroy(detach) {
 	this._fragment = this._state = null;
 }
 
-function differs(a, b) {
-	return a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+function _differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -151,7 +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;
 
@@ -189,7 +189,8 @@ var proto = {
 	_recompute: noop,
 	_set: _set,
 	_mount: _mount,
-	_unmount: _unmount
+	_unmount: _unmount,
+	_differs: _differs
 };
 
 /* generated by Svelte vX.Y.Z */
diff --git a/test/js/samples/window-binding-scroll/expected-bundle.js b/test/js/samples/window-binding-scroll/expected-bundle.js
index b310a6a839..a7c9026cc6 100644
--- a/test/js/samples/window-binding-scroll/expected-bundle.js
+++ b/test/js/samples/window-binding-scroll/expected-bundle.js
@@ -47,8 +47,8 @@ function destroy(detach) {
 	this._fragment = this._state = null;
 }
 
-function differs(a, b) {
-	return a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+function _differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
 }
 
 function dispatchObservers(component, group, changed, newState, oldState) {
@@ -147,7 +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;
 
@@ -185,7 +185,8 @@ var proto = {
 	_recompute: noop,
 	_set: _set,
 	_mount: _mount,
-	_unmount: _unmount
+	_unmount: _unmount,
+	_differs: _differs
 };
 
 /* generated by Svelte vX.Y.Z */
diff --git a/test/runtime/index.js b/test/runtime/index.js
index 778f47c0cc..aaafaff21b 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) {
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);
+		});
+	});
 });