bind to store values in simple cases - fixes #1997

src/compile/render-dom/wrappers/Element/Binding.ts

@@ -221,6 +221,17 @@ function getEventHandler(
 	snippet: string
 ) {
 	const value = getValueFromDom(renderer, binding.parent, binding);
+	const store = binding.object[0] === '$' ? binding.object.slice(1) : null;
+
+	if (store && binding.node.expression.node.type === 'MemberExpression') {
+		// TODO is there a way around this? Mutating an object doesn't work,
+		// because stores check for referential equality (i.e. immutable data).
+		// But we can't safely or easily clone objects. So for now, we bail
+		renderer.component.error(binding.node.expression.node.property, {
+			code: 'invalid-store-binding',
+			message: 'Cannot bind to a nested property of a store'
+		});
+	}
 
 	if (binding.node.isContextual) {
 		let tail = '';
@@ -233,15 +244,21 @@ function getEventHandler(
 
 		return {
 			usesContext: true,
-			mutation: `${snippet}${tail} = ${value};`,
+			mutation: store
+				? `${store}.set(${value});`
+				: `${snippet}${tail} = ${value};`,
 			contextual_dependencies: new Set([object, property])
 		};
 	}
 
+	const mutation = store
+		? `${store}.set(${value});`
+		: `${snippet} = ${value};`;
+
 	if (binding.node.expression.node.type === 'MemberExpression') {
 		return {
 			usesContext: binding.node.expression.usesContext,
-			mutation: `${snippet} = ${value};`,
+			mutation,
 			contextual_dependencies: binding.node.expression.contextual_dependencies,
 			snippet
 		};
@@ -249,7 +266,7 @@ function getEventHandler(
 
 	return {
 		usesContext: false,
-		mutation: `${snippet} = ${value};`,
+		mutation,
 		contextual_dependencies: new Set()
 	};
 }

src/compile/render-dom/wrappers/Element/index.ts

@@ -456,7 +456,7 @@ export default class ElementWrapper extends Wrapper {
 			this.renderer.component.partly_hoisted.push(deindent`
 				function ${handler}(${contextual_dependencies.size > 0 ? `{ ${[...contextual_dependencies].join(', ')} }` : ``}) {
 					${group.bindings.map(b => b.handler.mutation)}
-					${Array.from(dependencies).map(dep => `$$invalidate('${dep}', ${dep});`)}
+					${Array.from(dependencies).filter(dep => dep[0] !== '$').map(dep => `$$invalidate('${dep}', ${dep});`)}
 				}
 			`);
 

test/runtime/samples/binding-store-deep/_config.js

@@ -0,0 +1,5 @@
+export default {
+	error(assert, err) {
+		assert.equal(err.message, `Cannot bind to a nested property of a store`);
+	}
+};

test/runtime/samples/binding-store-deep/main.html

@@ -0,0 +1,8 @@
+<script>
+	import { writable } from 'svelte/store';
+
+	export const user = writable({ name: 'world' });
+</script>
+
+<input bind:value={$user.name}>
+<p>hello {$user.name}</p>

test/runtime/samples/binding-store/_config.js

@@ -0,0 +1,41 @@
+export default {
+	html: `
+		<input>
+		<p>hello world</p>
+	`,
+
+	ssrHtml: `
+		<input value="world">
+		<p>hello world</p>
+	`,
+
+	async test({ assert, component, target, window }) {
+		const input = target.querySelector('input');
+		assert.equal(input.value, 'world');
+
+		const event = new window.Event('input');
+
+		const names = [];
+		const unsubscribe = component.name.subscribe(name => {
+			names.push(name);
+		});
+
+		input.value = 'everybody';
+		await input.dispatchEvent(event);
+
+		assert.htmlEqual(target.innerHTML, `
+			<input>
+			<p>hello everybody</p>
+		`);
+
+		await component.name.set('goodbye');
+		assert.equal(input.value, 'goodbye');
+		assert.htmlEqual(target.innerHTML, `
+			<input>
+			<p>hello goodbye</p>
+		`);
+
+		assert.deepEqual(names, ['world', 'everybody', 'goodbye']);
+		unsubscribe();
+	},
+};

test/runtime/samples/binding-store/main.html

@@ -0,0 +1,8 @@
+<script>
+	import { writable } from 'svelte/store';
+
+	export const name = writable('world');
+</script>
+
+<input bind:value={$name}>
+<p>hello {$name}</p>