prevent stale state in component event handlers - fixes #1353

src/generators/nodes/Component.ts

@@ -10,6 +10,7 @@ import mungeAttribute from './shared/mungeAttribute';
 import Node from './shared/Node';
 import Block from '../dom/Block';
 import Attribute from './Attribute';
+import usesThisOrArguments from '../../validate/js/utils/usesThisOrArguments';
 
 export default class Component extends Node {
 	type: 'Component';
@@ -494,20 +495,24 @@ function mungeEventHandler(generator: DomGenerator, node: Node, handler: Node, b
 				);
 			}
 
+		let usesState = false;
+
 		handler.expression.arguments.forEach((arg: Node) => {
 			const { contexts } = block.contextualise(arg, null, true);
+			if (contexts.has('state')) usesState = true;
 
 			contexts.forEach(context => {
 				allContexts.add(context);
 			});
 		});
 
 		body = deindent`
+			${usesState && `const state = #component.get();`}
 			[✂${handler.expression.start}-${handler.expression.end}✂];
 		`;
 	} else {
 		body = deindent`
-			${block.alias('component')}.fire('${handler.name}', event);
+			#component.fire('${handler.name}', event);
 		`;
 	}
 

test/runtime/samples/component-event-not-stale/Button.html

@@ -0,0 +1 @@
+<button on:click><slot/></button>

test/runtime/samples/component-event-not-stale/_config.js

@@ -0,0 +1,30 @@
+export default {
+	data: {
+		value: 1,
+	},
+
+	test(assert, component, target, window) {
+		const buttons = target.querySelectorAll('button');
+		const click = new window.MouseEvent('click');
+
+		const events = [];
+		component.on('value', event => {
+			events.push(event);
+		});
+
+		buttons[0].dispatchEvent(click);
+		buttons[1].dispatchEvent(click);
+
+		component.set({ value: 2 });
+
+		buttons[0].dispatchEvent(click);
+		buttons[1].dispatchEvent(click);
+
+		assert.deepEqual(events, [
+			{ value: 1 },
+			{ value: 1 },
+			{ value: 2 },
+			{ value: 2 }
+		]);
+	},
+};

test/runtime/samples/component-event-not-stale/main.html

@@ -0,0 +1,20 @@
+<Button on:click="handleClick()">one</Button>
+<Button on:click="fire('value', {value})">two</Button>
+
+<script>
+	import Button from './Button.html';
+
+	export default {
+		components: {
+			Button
+		},
+
+		methods: {
+			handleClick() {
+				const { value } = this.get();
+				this.fire('value', { value });
+			}
+		}
+
+	}
+</script>