allow stores to work with mutable data - fixes #2171

store.mjs

@@ -1,14 +1,15 @@
-import { run_all, noop, get_store_value } from './internal';
+import { run_all, noop, get_store_value, safe_not_equal } from './internal';
 
 export function readable(start, value) {
 	const subscribers = [];
 	let stop;
 
-	function set(newValue) {
-		if (newValue === value) return;
-		value = newValue;
-		subscribers.forEach(s => s[1]());
-		subscribers.forEach(s => s[0](value));
+	function set(new_value) {
+		if (safe_not_equal(value, new_value)) {
+			value = new_value;
+			subscribers.forEach(s => s[1]());
+			subscribers.forEach(s => s[0](value));
+		}
 	}
 
 	return {
@@ -38,11 +39,12 @@ export function writable(value, start = noop) {
 	let stop;
 	const subscribers = [];
 
-	function set(newValue) {
-		if (newValue === value) return;
-		value = newValue;
-		subscribers.forEach(s => s[1]());
-		subscribers.forEach(s => s[0](value));
+	function set(new_value) {
+		if (safe_not_equal(value, new_value)) {
+			value = new_value;
+			subscribers.forEach(s => s[1]());
+			subscribers.forEach(s => s[0](value));
+		}
 	}
 
 	function update(fn) {

test/store/index.js

@@ -1,7 +1,7 @@
 import * as assert from 'assert';
 import { readable, writable, derive, get } from '../../store.js';
 
-describe('store', () => {
+describe.only('store', () => {
 	describe('writable', () => {
 		it('creates a writable store', () => {
 			const count = writable(0);
@@ -42,6 +42,23 @@ describe('store', () => {
 			unsubscribe2();
 			assert.equal(called, 0);
 		});
+
+		it('does not assume immutable data', () => {
+			const obj = {};
+			let called = 0;
+
+			const store = writable(obj);
+
+			store.subscribe(value => {
+				called += 1;
+			});
+
+			store.set(obj);
+			assert.equal(called, 2);
+
+			store.update(obj => obj);
+			assert.equal(called, 3);
+		});
 	});
 
 	describe('readable', () => {