feat dynamic event handler

src/compiler/compile/nodes/EventHandler.ts

@@ -1,8 +1,6 @@
 import Node from './shared/Node';
 import Expression from './shared/Expression';
 import Component from '../Component';
-import { b, x } from 'code-red';
-import Block from '../render_dom/Block';
 import { sanitize } from '../../utils/names';
 import { Identifier } from 'estree';
 
@@ -14,6 +12,7 @@ export default class EventHandler extends Node {
 	handler_name: Identifier;
 	uses_context = false;
 	can_make_passive = false;
+	reassigned?: boolean;
 
 	constructor(component: Component, parent, template_scope, info) {
 		super(component, parent, template_scope, info);
@@ -22,7 +21,7 @@ export default class EventHandler extends Node {
 		this.modifiers = new Set(info.modifiers);
 
 		if (info.expression) {
-			this.expression = new Expression(component, this, template_scope, info.expression, true);
+			this.expression = new Expression(component, this, template_scope, info.expression);
 			this.uses_context = this.expression.uses_context;
 
 			if (/FunctionExpression/.test(info.expression.type) && info.expression.params.length === 0) {
@@ -42,34 +41,12 @@ export default class EventHandler extends Node {
 					if (node && (node.type === 'FunctionExpression' || node.type === 'FunctionDeclaration' || node.type === 'ArrowFunctionExpression') && node.params.length === 0) {
 						this.can_make_passive = true;
 					}
+
+					this.reassigned = component.var_lookup.get(info.expression.name).reassigned;
 				}
 			}
 		} else {
-			const id = component.get_unique_name(`${sanitize(this.name)}_handler`);
-
-			component.add_var({
-				name: id.name,
-				internal: true,
-				referenced: true
-			});
-
-			component.partly_hoisted.push(b`
-				function ${id}(event) {
-					@bubble($$self, event);
-				}
-			`);
-
-			this.handler_name = id;
+			this.handler_name = component.get_unique_name(`${sanitize(this.name)}_handler`);
 		}
 	}
-
-	// TODO move this? it is specific to render-dom
-	render(block: Block) {
-		if (this.expression) {
-			return this.expression.manipulate(block);
-		}
-
-		// this.component.add_reference(this.handler_name);
-		return x`#ctx.${this.handler_name}`;
-	}
 }

src/compiler/compile/render_dom/Block.ts

@@ -203,13 +203,11 @@ export default class Block {
 	}
 
 	add_variable(id: Identifier, init?: Node) {
-		this.variables.forEach(v => {
-			if (v.id.name === id.name) {
-				throw new Error(
-					`Variable '${id.name}' already initialised with a different value`
-				);
-			}
-		});
+		if (this.variables.has(id.name)) {
+			throw new Error(
+				`Variable '${id.name}' already initialised with a different value`
+			);
+		}
 
 		this.variables.set(id.name, { id, init });
 	}

src/compiler/compile/render_dom/wrappers/Body.ts

@@ -3,21 +3,24 @@ import Wrapper from './shared/Wrapper';
 import { b } from 'code-red';
 import Body from '../../nodes/Body';
 import { Identifier } from 'estree';
+import EventHandler from './Element/EventHandler';
 
 export default class BodyWrapper extends Wrapper {
 	node: Body;
 
 	render(block: Block, _parent_node: Identifier, _parent_nodes: Identifier) {
-		this.node.handlers.forEach(handler => {
-			const snippet = handler.render(block);
+		this.node.handlers
+			.map(handler => new EventHandler(handler, this))
+			.forEach(handler => {
+				const snippet = handler.get_snippet(block);
 
-			block.chunks.init.push(b`
-				@_document.body.addEventListener("${handler.name}", ${snippet});
-			`);
+				block.chunks.init.push(b`
+					@_document.body.addEventListener("${handler.node.name}", ${snippet});
+				`);
 
-			block.chunks.destroy.push(b`
-				@_document.body.removeEventListener("${handler.name}", ${snippet});
-			`);
-		});
+				block.chunks.destroy.push(b`
+					@_document.body.removeEventListener("${handler.node.name}", ${snippet});
+				`);
+			});
 	}
 }

src/compiler/compile/render_dom/wrappers/Element/EventHandler.ts

@@ -0,0 +1,69 @@
+import EventHandler from '../../../nodes/EventHandler';
+import Wrapper from '../shared/Wrapper';
+import Block from '../../Block';
+import { b, x, p } from 'code-red';
+
+const TRUE = x`true`;
+const FALSE = x`false`;
+
+export default class EventHandlerWrapper {
+	node: EventHandler;
+	parent: Wrapper;
+
+	constructor(node: EventHandler, parent: Wrapper) {
+		this.node = node;
+		this.parent = parent;
+
+		if (!node.expression) {
+			this.parent.renderer.component.add_var({
+				name: node.handler_name.name,
+				internal: true,
+				referenced: true,
+			});
+
+			this.parent.renderer.component.partly_hoisted.push(b`
+        function ${node.handler_name.name}(event) {
+          @bubble($$self, event);
+        }
+      `);
+		}
+	}
+
+  get_snippet(block) {
+		const snippet = this.node.expression ? this.node.expression.manipulate(block) : x`#ctx.${this.node.handler_name}`;
+
+		if (this.node.reassigned) {
+			block.maintain_context = true;
+			return x`function () { ${snippet}.apply(this, arguments); }`;
+		}
+		return snippet;
+  }
+
+	render(block: Block, target: string) {
+		let snippet = this.get_snippet(block);
+
+    if (this.node.modifiers.has('preventDefault')) snippet = x`@prevent_default(${snippet})`;
+		if (this.node.modifiers.has('stopPropagation')) snippet = x`@stop_propagation(${snippet})`;
+		if (this.node.modifiers.has('self')) snippet = x`@self(${snippet})`;
+
+    const args = [];
+
+    const opts = ['passive', 'once', 'capture'].filter(mod => this.node.modifiers.has(mod));
+		if (opts.length) {
+			args.push((opts.length === 1 && opts[0] === 'capture')
+				? TRUE
+				: x`{ ${opts.map(opt => p`${opt}: true`)} }`);
+		} else if (block.renderer.options.dev) {
+			args.push(FALSE);
+		}
+
+		if (block.renderer.options.dev) {
+			args.push(this.node.modifiers.has('stopPropagation') ? TRUE : FALSE);
+			args.push(this.node.modifiers.has('preventDefault') ? TRUE : FALSE);
+		}
+
+    block.event_listeners.push(
+			x`@listen(${target}, "${this.node.name}", ${snippet}, ${args})`
+		);
+	}
+}

src/compiler/compile/render_dom/wrappers/Element/index.ts

@@ -24,6 +24,7 @@ import bind_this from '../shared/bind_this';
 import { changed } from '../shared/changed';
 import { is_head } from '../shared/is_head';
 import { Identifier } from 'estree';
+import EventHandler from './EventHandler';
 
 const events = [
 	{
@@ -113,6 +114,7 @@ export default class ElementWrapper extends Wrapper {
 	fragment: FragmentWrapper;
 	attributes: AttributeWrapper[];
 	bindings: Binding[];
+	event_handlers: EventHandler[];
 	class_dependencies: string[];
 
 	slot_block: Block;
@@ -194,6 +196,8 @@ export default class ElementWrapper extends Wrapper {
 		// e.g. <audio bind:paused bind:currentTime>
 		this.bindings = this.node.bindings.map(binding => new Binding(block, binding, this));
 
+		this.event_handlers = this.node.handlers.map(event_handler => new EventHandler(event_handler, this));
+
 		if (node.intro || node.outro) {
 			if (node.intro) block.add_intro(node.intro.is_local);
 			if (node.outro) block.add_outro(node.outro.is_local);
@@ -643,7 +647,7 @@ export default class ElementWrapper extends Wrapper {
 	}
 
 	add_event_handlers(block: Block) {
-		add_event_handlers(block, this.var, this.node.handlers);
+		add_event_handlers(block, this.var, this.event_handlers);
 	}
 
 	add_transitions(

src/compiler/compile/render_dom/wrappers/InlineComponent/index.ts

@@ -16,6 +16,7 @@ import is_dynamic from '../shared/is_dynamic';
 import bind_this from '../shared/bind_this';
 import { changed } from '../shared/changed';
 import { Node, Identifier, ObjectExpression } from 'estree';
+import EventHandler from '../Element/EventHandler';
 
 export default class InlineComponentWrapper extends Wrapper {
 	var: Identifier;
@@ -365,7 +366,8 @@ export default class InlineComponentWrapper extends Wrapper {
 		});
 
 		const munged_handlers = this.node.handlers.map(handler => {
-			let snippet = handler.render(block);
+			const event_handler = new EventHandler(handler, this);
+			let snippet = event_handler.get_snippet(block);
 			if (handler.modifiers.has('once')) snippet = x`@once(${snippet})`;
 
 			return b`${name}.$on("${handler.name}", ${snippet});`;

src/compiler/compile/render_dom/wrappers/Window.ts

@@ -8,6 +8,7 @@ import add_actions from './shared/add_actions';
 import { changed } from './shared/changed';
 import { Identifier } from 'estree';
 import { TemplateNode } from '../../../interfaces';
+import EventHandler from './Element/EventHandler';
 
 const associated_events = {
 	innerWidth: 'resize',
@@ -34,9 +35,11 @@ const readonly = new Set([
 
 export default class WindowWrapper extends Wrapper {
 	node: Window;
+	handlers: EventHandler[];
 
 	constructor(renderer: Renderer, block: Block, parent: Wrapper, node: TemplateNode) {
 		super(renderer, block, parent, node);
+		this.handlers = this.node.handlers.map(handler => new EventHandler(handler, this));
 	}
 
 	render(block: Block, _parent_node: Identifier, _parent_nodes: Identifier) {
@@ -47,7 +50,7 @@ export default class WindowWrapper extends Wrapper {
 		const bindings: Record<string, string> = {};
 
 		add_actions(component, block, '@_window', this.node.actions);
-		add_event_handlers(block, '@_window', this.node.handlers);
+		add_event_handlers(block, '@_window', this.handlers);
 
 		this.node.bindings.forEach(binding => {
 			// in dev mode, throw if read-only values are written to

src/compiler/compile/render_dom/wrappers/shared/add_event_handlers.ts

@@ -1,39 +1,10 @@
 import Block from '../../Block';
-import EventHandler from '../../../nodes/EventHandler';
-import { x, p } from 'code-red';
-
-const TRUE = x`true`;
-const FALSE = x`false`;
+import EventHandler from '../Element/EventHandler';
 
 export default function add_event_handlers(
 	block: Block,
 	target: string,
 	handlers: EventHandler[]
 ) {
-	handlers.forEach(handler => {
-		let snippet = handler.render(block);
-		if (handler.modifiers.has('preventDefault')) snippet = x`@prevent_default(${snippet})`;
-		if (handler.modifiers.has('stopPropagation')) snippet = x`@stop_propagation(${snippet})`;
-		if (handler.modifiers.has('self')) snippet = x`@self(${snippet})`;
-
-		const args = [];
-
-		const opts = ['passive', 'once', 'capture'].filter(mod => handler.modifiers.has(mod));
-		if (opts.length) {
-			args.push((opts.length === 1 && opts[0] === 'capture')
-				? TRUE
-				: x`{ ${opts.map(opt => p`${opt}: true`)} }`);
-		} else if (block.renderer.options.dev) {
-			args.push(FALSE);
-		}
-
-		if (block.renderer.options.dev) {
-			args.push(handler.modifiers.has('stopPropagation') ? TRUE : FALSE);
-			args.push(handler.modifiers.has('preventDefault') ? TRUE : FALSE);
-		}
-
-		block.event_listeners.push(
-			x`@listen(${target}, "${handler.name}", ${snippet}, ${args})`
-		);
-	});
+	handlers.forEach(handler => handler.render(block, target));
 }