preserve arrow function event handlers

src/compiler/compile/nodes/shared/Expression.ts

@@ -322,15 +322,11 @@ export default class Expression {
 						args.push(original_params);
 					}
 
-					// TODO is this still necessary?
-					let body = code.slice(node.body.start, node.body.end).trim();
-					if (node.body.type !== 'BlockStatement') {
-						body = `{\n\treturn ${body};\n}`;
-					}
+					const body = code.slice(node.body.start, node.body.end).trim();
 
-					const fn = deindent`
-						${node.async && 'async '}function${node.generator && '*'} ${name}(${args.join(', ')}) ${body}
-					`;
+					const fn = node.type === 'FunctionExpression'
+						? `${node.async ? 'async ' : ''}function${node.generator ? '*' : ''} ${name}(${args.join(', ')}) ${body}`
+						: `const ${name} = ${node.async ? 'async ' : ''}(${args.join(', ')}) => ${body};`;
 
 					if (dependencies.size === 0 && contextual_dependencies.size === 0) {
 						// we can hoist this out of the component completely

test/js/samples/action-custom-event-handler/expected.js

@@ -53,9 +53,7 @@ function foo(node, callback) {
 function instance($$self, $$props, $$invalidate) {
 	let { bar } = $$props;
 
-	function foo_function() {
-		return handleFoo(bar);
-	}
+	const foo_function = () => handleFoo(bar);
 
 	$$self.$set = $$props => {
 		if ('bar' in $$props) $$invalidate('bar', bar = $$props.bar);

test/js/samples/dynamic-import/expected.js

@@ -46,9 +46,7 @@ function create_fragment(ctx) {
 	};
 }
 
-function func() {
-	return import('./Foo.svelte');
-}
+const func = () => import('./Foo.svelte');
 
 class Component extends SvelteComponent {
 	constructor(options) {

test/js/samples/event-handler-no-passive/expected.js

@@ -40,9 +40,7 @@ function create_fragment(ctx) {
 	};
 }
 
-function touchstart_handler(e) {
-	return e.preventDefault();
-}
+const touchstart_handler = (e) => e.preventDefault();
 
 class Component extends SvelteComponent {
 	constructor(options) {

test/js/samples/instrumentation-template-if-no-block/expected.js

@@ -60,9 +60,9 @@ function create_fragment(ctx) {
 function instance($$self, $$props, $$invalidate) {
 	let x = 0;
 
-	function click_handler() {
+	const click_handler = () => {
 		if (true) $$invalidate('x', x += 1);
-	}
+	};
 
 	return { x, click_handler };
 }

test/js/samples/instrumentation-template-x-equals-x/expected.js

@@ -60,7 +60,7 @@ function create_fragment(ctx) {
 function instance($$self, $$props, $$invalidate) {
 	let things = [];
 
-	function click_handler() { things.push(1); $$invalidate('things', things) }
+	const click_handler = () => { things.push(1); $$invalidate('things', things) };
 
 	return { things, click_handler };
 }