diff --git a/site/src/components/Repl/CodeMirror.svelte b/site/src/components/Repl/CodeMirror.svelte
index 839665bbc6..a51b532565 100644
--- a/site/src/components/Repl/CodeMirror.svelte
+++ b/site/src/components/Repl/CodeMirror.svelte
@@ -13,12 +13,11 @@
 
 <script>
 	import { onMount, beforeUpdate, createEventDispatcher, getContext } from 'svelte';
+	import Message from './Message.svelte';
 
 	const dispatch = createEventDispatcher();
 	const { navigate } = getContext('REPL');
 
-	export let mode;
-	export let code;
 	export let readonly = false;
 	export let errorLoc = null;
 	export let flex = false;
@@ -27,17 +26,46 @@
 
 	let w;
 	let h;
+	let code = '';
+	let mode;
+
+	// We have to expose set and update methods, rather
+	// than making this state-driven through props,
+	// because it's difficult to update an editor
+	// without resetting scroll otherwise
+	export function set(new_code, new_mode) {
+		if (new_mode !== mode) {
+			createEditor(mode = new_mode);
+		}
+
+		code = new_code;
+		if (editor) editor.setValue(code);
+	}
+
+	export function update(new_code) {
+		code = new_code;
+
+		if (editor) {
+			const { left, top } = editor.getScrollInfo();
+			editor.setValue(code = new_code);
+			editor.scrollTo(left, top);
+		}
+	}
 
 	export function resize() {
 		editor.refresh();
 	}
 
 	const modes = {
+		js: {
+			name: 'javascript',
+			json: false
+		},
 		json: {
 			name: 'javascript',
 			json: true
 		},
-		handlebars: {
+		svelte: {
 			name: 'handlebars',
 			base: 'text/html'
 		}
@@ -51,15 +79,6 @@
 	let destroyed = false;
 	let CodeMirror;
 
-	$: if (CodeMirror) {
-		createEditor(mode);
-	}
-
-	$: if (editor && !updating && code != null) {
-		updating = true;
-		editor.setValue(code);
-	}
-
 	$: if (editor && w && h) {
 		editor.refresh();
 	}
@@ -96,9 +115,13 @@
 	onMount(() => {
 		if (_CodeMirror) {
 			CodeMirror = _CodeMirror;
+			createEditor(mode || 'svelte');
+			editor.setValue(code || '');
 		} else {
 			codemirror_promise.then(mod => {
 				CodeMirror = mod.default;
+				createEditor(mode || 'svelte');
+				editor.setValue(code || '');
 			});
 		}
 
@@ -113,7 +136,7 @@
 	});
 
 	function createEditor(mode) {
-		if (destroyed) return;
+		if (destroyed || !CodeMirror) return;
 
 		if (editor) {
 			editor.toTextArea();
@@ -125,7 +148,7 @@
 			indentWithTabs: true,
 			indentUnit: 2,
 			tabSize: 2,
-			value: code,
+			value: '',
 			mode: modes[mode] || {
 				name: mode
 			},
@@ -142,8 +165,8 @@
 		editor.on('change', instance => {
 			if (!updating) {
 				updating = true;
-				code = instance.getValue();
-				dispatch('change', { value: code });
+				// code = instance.getValue();
+				dispatch('change', { value: instance.getValue() });
 			}
 		});
 
@@ -254,6 +277,8 @@
 		<pre style="position: absolute; left: 0; top: 0"
 		>{code}</pre>
 
-		<p class='loading message'>loading editor...</p>
+		<div style="position: absolute; width: 100%; bottom: 0">
+			<Message kind='info'>loading editor...</Message>
+		</div>
 	{/if}
 </div>
\ No newline at end of file
diff --git a/site/src/components/Repl/Input/ComponentSelector.svelte b/site/src/components/Repl/Input/ComponentSelector.svelte
index 54212014fa..02511c373d 100644
--- a/site/src/components/Repl/Input/ComponentSelector.svelte
+++ b/site/src/components/Repl/Input/ComponentSelector.svelte
@@ -3,16 +3,17 @@
 	import Icon from '../../Icon.svelte';
 	import { enter } from '../../../utils/events.js';
 
+	export let handle_select;
+
 	const { components, selected } = getContext('REPL');
 
 	let editing = null;
 
 	function selectComponent(component) {
-		if ($selected != component) {
+		if ($selected !== component) {
 			editing = null;
+			handle_select(component);
 		}
-
-		selected.set(component);
 	}
 
 	function editTab(component) {
diff --git a/site/src/components/Repl/Input/ModuleEditor.svelte b/site/src/components/Repl/Input/ModuleEditor.svelte
index e7a9dc9059..e7a3a0e6c7 100644
--- a/site/src/components/Repl/Input/ModuleEditor.svelte
+++ b/site/src/components/Repl/Input/ModuleEditor.svelte
@@ -1,27 +1,16 @@
 <script>
-	import { getContext } from 'svelte';
+	import { getContext, onMount } from 'svelte';
 	import CodeMirror from '../CodeMirror.svelte';
 	import Message from '../Message.svelte';
 
-	const { selected, handle_change, navigate } = getContext('REPL');
+	const { bundle, selected, handle_change, navigate, register_module_editor } = getContext('REPL');
 
-	export let error;
 	export let errorLoc;
-	export let warnings;
 
-	$: message = warning => {
-		let str = warning.message;
-
-		let loc = [];
-
-		if (warning.filename && warning.filename !== `${$selected.name}.${$selected.type}`) {
-			loc.push(warning.filename);
-		}
-
-		if (warning.start) loc.push(warning.start.line, warning.start.column);
-
-		return str + (loc.length ? ` (${loc.join(':')})` : ``);
-	};
+	let editor;
+	onMount(() => {
+		register_module_editor(editor);
+	});
 </script>
 
 <style>
@@ -49,23 +38,22 @@
 
 <div class="editor-wrapper">
 	<div class="editor">
-		{#if $selected}
-			<CodeMirror
-				mode="{$selected.type === 'js' ? 'javascript' : 'handlebars'}"
-				code={$selected.source}
-				{errorLoc}
-				on:change={handle_change}
-			/>
-		{/if}
+		<CodeMirror
+			bind:this={editor}
+			{errorLoc}
+			on:change={handle_change}
+		/>
 	</div>
 
 	<div class="info">
-		{#if error}
-			<Message kind="error" details={error} filename="{$selected.name}.{$selected.type}"/>
-		{:else if warnings.length > 0}
-			{#each warnings as warning}
-				<Message kind="warning" details={warning} filename="{$selected.name}.{$selected.type}"/>
-			{/each}
+		{#if $bundle}
+			{#if $bundle.error}
+				<Message kind="error" details={$bundle.error} filename="{$selected.name}.{$selected.type}"/>
+			{:else if $bundle.warnings.length > 0}
+				{#each $bundle.warnings as warning}
+					<Message kind="warning" details={warning} filename="{$selected.name}.{$selected.type}"/>
+				{/each}
+			{/if}
 		{/if}
 	</div>
 </div>
\ No newline at end of file
diff --git a/site/src/components/Repl/Message.svelte b/site/src/components/Repl/Message.svelte
index c8f2183827..6a9183dfb3 100644
--- a/site/src/components/Repl/Message.svelte
+++ b/site/src/components/Repl/Message.svelte
@@ -4,8 +4,8 @@
 	const { navigate } = getContext('REPL');
 
 	export let kind;
-	export let details;
-	export let filename;
+	export let details = null;
+	export let filename = null;
 
 	function message(details) {
 		let str = details.message || '[missing message]';
diff --git a/site/src/components/Repl/Output/Compiler.js b/site/src/components/Repl/Output/Compiler.js
new file mode 100644
index 0000000000..b6d13e53bd
--- /dev/null
+++ b/site/src/components/Repl/Output/Compiler.js
@@ -0,0 +1,38 @@
+export default class Compiler {
+	constructor(version) {
+		this.worker = new Worker('/workers/compiler.js');
+		this.worker.postMessage({ type: 'init', version });
+
+		this.uid = 1;
+		this.handlers = new Map();
+
+		this.worker.onmessage = event => {
+			const handler = this.handlers.get(event.data.id);
+			handler(event.data.result);
+			this.handlers.delete(event.data.id);
+		};
+	}
+
+	compile(component, options) {
+		return new Promise(fulfil => {
+			const id = this.uid++;
+
+			this.handlers.set(id, fulfil);
+
+			this.worker.postMessage({
+				id,
+				type: 'compile',
+				source: component.source,
+				options: Object.assign({
+					name: component.name,
+					filename: `${component.name}.svelte`
+				}, options),
+				entry: component.name === 'App'
+			});
+		});
+	}
+
+	destroy() {
+		this.worker.terminate();
+	}
+}
\ No newline at end of file
diff --git a/site/src/components/Repl/Output/Viewer.svelte b/site/src/components/Repl/Output/Viewer.svelte
index 23c228cd3a..1e02e69d2e 100644
--- a/site/src/components/Repl/Output/Viewer.svelte
+++ b/site/src/components/Repl/Output/Viewer.svelte
@@ -44,7 +44,6 @@
 		});
 
 		return () => {
-			proxy.eval(`if (window.component) window.component.\$destroy();`)
 			proxy.destroy();
 		}
 	});
diff --git a/site/src/components/Repl/Output/index.svelte b/site/src/components/Repl/Output/index.svelte
index 5d8fa4be45..884d38efdb 100644
--- a/site/src/components/Repl/Output/index.svelte
+++ b/site/src/components/Repl/Output/index.svelte
@@ -1,24 +1,69 @@
 <script>
-	import { getContext } from 'svelte';
+	import { getContext, onMount } from 'svelte';
 	import SplitPane from '../SplitPane.svelte';
 	import Viewer from './Viewer.svelte';
 	import CompilerOptions from './CompilerOptions.svelte';
+	import Compiler from './Compiler.js';
 	import PropEditor from './PropEditor.svelte';
 	import CodeMirror from '../CodeMirror.svelte';
 
-	const { bundle, values } = getContext('REPL');
+	const { values, register_output } = getContext('REPL');
 
-	export let js;
-	export let css;
-	export let props;
+	export let version;
 	export let sourceErrorLoc;
 	export let runtimeError;
-	export let compile_options;
 	export let embedded;
 	export let show_props;
 
+	let props;
+
+	let compile_options = {
+		generate: 'dom',
+		dev: false,
+		css: false,
+		hydratable: false,
+		customElement: false,
+		immutable: false,
+		legacy: false
+	};
+
+	register_output({
+		set: async selected => {
+			if (selected.type === 'js') {
+				js_editor.set(`/* Select a component to see its compiled code */`);
+				css_editor.set(`/* Select a component to see its compiled code */`);
+				return;
+			}
+
+			const compiled = await compiler.compile(selected, compile_options);
+
+			js_editor.set(compiled.js, 'js');
+			css_editor.set(compiled.css, 'css');
+			if (compiled.props) props = compiled.props;
+		},
+
+		update: async selected => {
+			if (selected.type === 'js') return;
+
+			const compiled = await compiler.compile(selected, compile_options);
+
+			js_editor.update(compiled.js);
+			css_editor.update(compiled.css);
+			if (compiled.props) props = compiled.props;
+		}
+	});
+
+	let compiler;
+
+	onMount(() => {
+		compiler = new Compiler(version);
+		return () => compiler.destroy();
+	});
+
 	// refs
 	let viewer;
+	let js_editor;
+	let css_editor;
 	const setters = {};
 
 	let view = 'result';
@@ -94,6 +139,20 @@
 	.props code {
 		top: .1rem;
 	}
+
+	.tab-content {
+		position: absolute;
+		width: 100%;
+		height: 100%;
+		opacity: 0;
+		pointer-events: none;
+	}
+
+	.tab-content.visible {
+		/* can't use visibility due to a weird painting bug in Chrome */
+		opacity: 1;
+		pointer-events: all;
+	}
 </style>
 
 <div class="view-toggle">
@@ -113,7 +172,8 @@
 	>CSS output</button>
 </div>
 
-{#if view === 'result'}
+<!-- component viewer -->
+<div class="tab-content" class:visible="{view === 'result'}">
 	<SplitPane type="vertical" pos={67} fixed={!show_props} fixed_pos={100}>
 		<div slot="a">
 			<Viewer
@@ -152,28 +212,43 @@
 			{/if}
 		</section>
 	</SplitPane>
-{:else if embedded}
+</div>
+
+<!-- js output -->
+<div class="tab-content" class:visible="{view === 'js'}">
+	{#if embedded}
+		<CodeMirror
+			bind:this={js_editor}
+			mode="js"
+			errorLoc={sourceErrorLoc}
+			readonly
+		/>
+	{:else}
+		<SplitPane type="vertical" pos={67}>
+			<div slot="a">
+				<CodeMirror
+					bind:this={js_editor}
+					mode="js"
+					errorLoc={sourceErrorLoc}
+					readonly
+				/>
+			</div>
+
+			<section slot="b">
+				<h3>Compiler options</h3>
+
+				<CompilerOptions bind:options={compile_options}/>
+			</section>
+		</SplitPane>
+	{/if}
+</div>
+
+<!-- css output -->
+<div class="tab-content" class:visible="{view === 'css'}">
 	<CodeMirror
-		mode="javascript"
-		code="{view === 'js' ? js : css}"
+		bind:this={css_editor}
+		mode="css"
 		errorLoc={sourceErrorLoc}
 		readonly
 	/>
-{:else}
-	<SplitPane type="vertical" pos={67}>
-		<div slot="a">
-			<CodeMirror
-				mode="javascript"
-				code="{view === 'js' ? js : css}"
-				errorLoc={sourceErrorLoc}
-				readonly
-			/>
-		</div>
-
-		<section slot="b">
-			<h3>Compiler options</h3>
-
-			<CompilerOptions bind:options={compile_options}/>
-		</section>
-	</SplitPane>
-{/if}
+</div>
\ No newline at end of file
diff --git a/site/src/components/Repl/index.svelte b/site/src/components/Repl/index.svelte
index c58e3d22bc..6b351f8535 100644
--- a/site/src/components/Repl/index.svelte
+++ b/site/src/components/Repl/index.svelte
@@ -1,7 +1,6 @@
 <script>
 	import { onMount, setContext } from 'svelte';
 	import { writable } from 'svelte/store';
-	import * as fleece from 'golden-fleece';
 	import SplitPane from './SplitPane.svelte';
 	import CodeMirror from './CodeMirror.svelte';
 	import ComponentSelector from './Input/ComponentSelector.svelte';
@@ -10,7 +9,6 @@
 	import InputOutputToggle from './InputOutputToggle.svelte';
 
 	export let version = 'beta'; // TODO change this to latest when the time comes
-	export let app;
 	export let embedded = false;
 	export let orientation = 'columns';
 	export let show_props = true;
@@ -23,14 +21,37 @@
 		version; // workaround
 
 		return {
-			imports,
+			imports: $bundle.imports,
 			components: $components,
 			values: $values
 		};
 	}
 
-	export function update(app) {
-		// TODO
+	export function set(data) {
+		components.set(data.components);
+		values.set(data.values);
+		selected.set(data.components[0]);
+
+		module_editor.set($selected.source, $selected.type);
+		output.set($selected);
+	}
+
+	export function update(data) {
+		const { name, type } = $selected || {};
+
+		components.set(data.components);
+		values.set(data.values);
+
+		const matched_component = data.components.find(file => file.name === name && file.type === type);
+		selected.set(matched_component || data.components[0]);
+
+		if (matched_component) {
+			module_editor.update(matched_component.source);
+			output.update(matched_component);
+		} else {
+			module_editor.set(matched_component.source, matched_component.type);
+			output.set(matched_component);
+		}
 	}
 
 	const components = writable([]);
@@ -38,6 +59,9 @@
 	const selected = writable(null);
 	const bundle = writable(null);
 
+	let module_editor;
+	let output;
+
 	setContext('REPL', {
 		components,
 		values,
@@ -52,6 +76,8 @@
 			const component = $components.find(c => c.name === name && c.type === type);
 			selected.set(component);
 
+			output.set($selected);
+
 			// TODO select the line/column in question
 		},
 
@@ -69,109 +95,59 @@
 			components.update(c => c);
 
 			// recompile selected component
-			compile($selected, compile_options);
+			output.update($selected);
 
 			// regenerate bundle (TODO do this in a separate worker?)
 			workers.bundler.postMessage({ type: 'bundle', components: $components });
+		},
+
+		register_module_editor(editor) {
+			module_editor = editor;
+		},
+
+		register_output(handlers) {
+			output = handlers;
 		}
 	});
 
-	$: {
-		components.set(app.components);
-		values.set(app.values);
-		selected.set(app.components[0]);
+	function handle_select(component) {
+		selected.set(component);
+		module_editor.set(component.source, component.type);
+		output.set($selected);
 	}
 
 	let workers;
 
-	let imports = null;
-	let import_map = null;
-	let dom;
-	let ssr;
-	let sourceError = null;
-	let runtimeError = null;
-	let warnings = [];
-	let js = '';
-	let css = '';
-	let uid = 0;
-	let props = [];
+	let input;
 	let sourceErrorLoc;
-	let runtimeErrorLoc;
-
-	let compile_options = {
-		generate: 'dom',
-		dev: false,
-		css: false,
-		hydratable: false,
-		customElement: false,
-		immutable: false,
-		legacy: false
-	};
+	let runtimeErrorLoc; // TODO refactor this stuff — runtimeErrorLoc is unused
 
 	let width = typeof window !== 'undefined' ? window.innerWidth : 300;
 	let show_output = false;
 
 	onMount(async () => {
 		workers = {
-			compiler: new Worker('/workers/compiler.js'),
 			bundler: new Worker('/workers/bundler.js')
 		};
 
-		workers.compiler.postMessage({ type: 'init', version });
-		workers.compiler.onmessage = event => {
-			js = event.data.js;
-			css = event.data.css || `/* Add a <sty` + `le> tag to see compiled CSS */`;
-			if (event.data.props) props = event.data.props;
-		};
-
 		workers.bundler.postMessage({ type: 'init', version });
 		workers.bundler.onmessage = event => {
 			bundle.set(event.data);
-			({ imports, import_map, dom, ssr, warnings, error: sourceError } = event.data);
-			if (sourceError) console.error(sourceError);
-			runtimeError = null;
 		};
 
 		return () => {
-			workers.compiler.terminate();
 			workers.bundler.terminate();
 		};
 	});
 
-	function compile(component, options) {
-		if (component.type === 'svelte') {
-			workers.compiler.postMessage({
-				type: 'compile',
-				source: component.source,
-				options: Object.assign({
-					name: component.name,
-					filename: `${component.name}.svelte`
-				}, options),
-				entry: component === $components[0]
-			});
-		} else {
-			js = css = `/* Select a component to see its compiled code */`;
-		}
-	}
-
-	$: if (sourceError && $selected) {
-		sourceErrorLoc = sourceError.filename === `${$selected.name}.${$selected.type}`
-			? sourceError.start
-			: null;
-	}
-
-	$: if (runtimeError && $selected) {
-		runtimeErrorLoc = runtimeError.filename === `${$selected.name}.${$selected.type}`
-			? runtimeError.start
+	$: if ($bundle && $bundle.error && $selected) {
+		sourceErrorLoc = $bundle.error.filename === `${$selected.name}.${$selected.type}`
+			? $bundle.error.start
 			: null;
 	}
 
-	$: if (workers && app.components) {
-		workers.bundler.postMessage({ type: 'bundle', components: app.components });
-	}
-
-	$: if (workers && $selected) {
-		compile($selected, compile_options);
+	$: if (workers && $components) {
+		workers.bundler.postMessage({ type: 'bundle', components: $components });
 	}
 </script>
 
@@ -240,21 +216,12 @@
 			fixed_pos={50}
 		>
 			<section slot=a>
-				<ComponentSelector/>
-				<ModuleEditor error={sourceError} errorLoc="{sourceErrorLoc || runtimeErrorLoc}" {warnings}/>
+				<ComponentSelector {handle_select}/>
+				<ModuleEditor bind:this={input} errorLoc="{sourceErrorLoc || runtimeErrorLoc}"/>
 			</section>
 
 			<section slot=b style='height: 100%;'>
-				<Output
-					bind:compile_options
-					{version}
-					{js}
-					{css}
-					{props}
-					{runtimeError}
-					{embedded}
-					{show_props}
-				/>
+				<Output {version} {embedded} {show_props}/>
 			</section>
 		</SplitPane>
 	</div>
diff --git a/site/src/routes/repl/embed.svelte b/site/src/routes/repl/embed.svelte
index 305fabc7aa..fc74d8df5f 100644
--- a/site/src/routes/repl/embed.svelte
+++ b/site/src/routes/repl/embed.svelte
@@ -15,11 +15,7 @@
 
 	export let version, gist, demo;
 
-	let app = {
-		components: [],
-		values: {}
-	};
-
+	let repl;
 	let name = 'loading...';
 
 	onMount(() => {
@@ -67,7 +63,7 @@
 						return a.name < b.name ? -1 : 1;
 					});
 
-				app = { components, values };
+				repl.set({ components, values });
 			});
 		} else if (demo) {
 			const url = `api/examples/${demo}`;
@@ -76,10 +72,10 @@
 				if (response.ok) {
 					const data = await response.json();
 
-					app = {
+					repl.set({
 						values: tryParseData(data.json5) || {}, // TODO make this more error-resistant
 						components: data.components
-					};
+					});
 				}
 			});
 		}
@@ -114,6 +110,6 @@
 
 <div class="repl-outer">
 	{#if process.browser}
-		<Repl {version} {app} embedded={true}/>
+		<Repl bind:this={repl} {version} embedded={true}/>
 	{/if}
 </div>
diff --git a/site/src/routes/repl/index.svelte b/site/src/routes/repl/index.svelte
index 90741ae8bb..4adf5368d0 100644
--- a/site/src/routes/repl/index.svelte
+++ b/site/src/routes/repl/index.svelte
@@ -18,16 +18,10 @@
 
 	export let version, demo, gist_id;
 
+	let repl;
 	let gist;
-
-	let app = {
-		components: [],
-		values: {}
-	};
-
 	let name = 'loading...';
 	let zen_mode = false;
-	let repl;
 
 	$: if (typeof history !== 'undefined') {
 		const params = [];
@@ -99,7 +93,7 @@
 						return a.name < b.name ? -1 : 1;
 					});
 
-				app = { components, values };
+				repl.set({ components, values });
 			});
 		}
 	});
@@ -117,10 +111,10 @@
 
 				console.log(data.components);
 
-				app = {
+				repl.set({
 					values: tryParseData(data.json5) || {}, // TODO make this more error-resistant
 					components: data.components
-				};
+				});
 
 				gist = null;
 			}
@@ -198,7 +192,6 @@
 <div class="repl-outer {zen_mode ? 'zen-mode' : ''}">
 	<AppControls
 		{examples}
-		{app}
 		{name}
 		{gist}
 		{repl}
@@ -208,6 +201,6 @@
 	/>
 
 	{#if process.browser}
-		<Repl bind:this={repl} {version} {app}/>
+		<Repl bind:this={repl} {version}/>
 	{/if}
 </div>
diff --git a/site/src/routes/tutorial/[slug]/index.svelte b/site/src/routes/tutorial/[slug]/index.svelte
index 514853177c..eb2ab246a4 100644
--- a/site/src/routes/tutorial/[slug]/index.svelte
+++ b/site/src/routes/tutorial/[slug]/index.svelte
@@ -24,8 +24,9 @@
 
 	const { sections } = getContext('tutorial');
 
-	const lookup = new Map();
+	let repl;
 	let prev;
+	const lookup = new Map();
 
 	sections.forEach(section => {
 		section.chapters.forEach(chapter => {
@@ -52,27 +53,24 @@
 	$: selected = lookup.get(slug);
 	$: improve_link = `${tutorial_repo_link}/${selected.chapter.section_dir}/${selected.chapter.chapter_dir}`;
 
-	// TODO once reactive values are fixed
-	// $: app = {
-	// 	components: chapter.app_a,
-	// 	values: {}
-	// };
-
-	let app;
-	$: start(chapter);
+	const clone = file => ({
+		name: file.name,
+		type: file.type,
+		source: file.source
+	});
 
-	function start(chapter) {
-		app = {
-			components: chapter.app_a,
+	$: if (repl) {
+		repl.set({
+			components: chapter.app_a.map(clone),
 			values: {}
-		};
+		});
 	}
 
 	function complete() {
-		app = {
-			components: chapter.app_b,
+		repl.update({
+			components: chapter.app_b.map(clone),
 			values: {}
-		};
+		});
 	}
 </script>
 
@@ -232,6 +230,6 @@
 	</div>
 
 	<div class="tutorial-repl">
-		<Repl {app} orientation="rows" show_props={false}/>
+		<Repl bind:this={repl} orientation="rows" show_props={false}/>
 	</div>
 </div>
diff --git a/site/static/workers/compiler.js b/site/static/workers/compiler.js
index 0583186dc7..d234c2a0bb 100644
--- a/site/static/workers/compiler.js
+++ b/site/static/workers/compiler.js
@@ -29,7 +29,7 @@ const commonCompilerOptions = {
 	css: false
 };
 
-function compile({ source, options, entry }) {
+function compile({ id, source, options, entry }) {
 	try {
 		const { js, css, stats, vars } = svelte.compile(
 			source,
@@ -40,11 +40,26 @@ function compile({ source, options, entry }) {
 			? (vars || stats.vars).map(v => v.writable && v.export_name).filter(Boolean) // TODO remove stats post-launch
 			: null;
 
-		return { js: js.code, css: css.code, props };
+		return {
+			id,
+			result: {
+				js: js.code,
+				css: css.code || `/* Add a <sty` + `le> tag to see compiled CSS */`,
+				props
+			}
+		};
 	} catch (err) {
-		let result = `/* Error compiling component\n\n${err.message}`;
-		if (err.frame) result += `\n${err.frame}`;
-		result += `\n\n*/`;
-		return { code: result, props: null };
+		let message = `/* Error compiling component\n\n${err.message}`;
+		if (err.frame) message += `\n${err.frame}`;
+		message += `\n\n*/`;
+
+		return {
+			id,
+			result: {
+				js: message,
+				css: message,
+				props: null
+			}
+		};
 	}
 }