diff --git a/site/.eslintrc.json b/site/.eslintrc.json
new file mode 100644
index 0000000000..cb0d06a2ec
--- /dev/null
+++ b/site/.eslintrc.json
@@ -0,0 +1,45 @@
+{
+	"root": true,
+	"rules": {
+		"indent": [2, "tab", { "SwitchCase": 1 }],
+		"semi": [2, "always"],
+		"keyword-spacing": [2, { "before": true, "after": true }],
+		"space-before-blocks": [2, "always"],
+		"no-mixed-spaces-and-tabs": [2, "smart-tabs"],
+		"no-cond-assign": 0,
+		"no-unused-vars": 2,
+		"object-shorthand": [2, "always"],
+		"no-const-assign": 2,
+		"no-class-assign": 2,
+		"no-this-before-super": 2,
+		"no-var": 2,
+		"no-unreachable": 2,
+		"valid-typeof": 2,
+		"quote-props": [2, "as-needed"],
+		"one-var": [2, "never"],
+		"prefer-arrow-callback": 2,
+		"prefer-const": [2, { "destructuring": "all" }],
+		"arrow-spacing": 2,
+		"no-inner-declarations": 0
+	},
+	"env": {
+		"es6": true,
+		"browser": true,
+		"node": true,
+		"mocha": true
+	},
+	"extends": [
+		"eslint:recommended",
+		"plugin:import/errors",
+		"plugin:import/warnings"
+	],
+	"plugins": ["svelte3"],
+	"parserOptions": {
+		"ecmaVersion": 6,
+		"sourceType": "module"
+	},
+	"settings": {
+		"import/core-modules": ["svelte"],
+		"svelte3/extensions": [".html"]
+	}
+}
diff --git a/site/content/examples/line-chart/App.html b/site/content/examples/line-chart/App.html
index d5d83ec49c..41881f8a8f 100644
--- a/site/content/examples/line-chart/App.html
+++ b/site/content/examples/line-chart/App.html
@@ -23,7 +23,7 @@
 		.domain([minX, maxX])
 		.range([padding.left, width - padding.right]);
 
-	$: yScale = scaleLinear
+	$: yScale = scaleLinear()
 		.domain([Math.min.apply(null, yTicks), Math.max.apply(null, yTicks)])
 		.range([height - padding.bottom, padding.top]);
 
@@ -50,7 +50,7 @@
 <div class="chart">
 	<h2>Arctic sea ice minimum</h2>
 
-	<svg ref:svg>
+	<svg bind:this={svg}>
 		<!-- y axis -->
 		<g class="axis y-axis" transform="translate(0, {padding.top})">
 			{#each yTicks as tick}
diff --git a/site/package-lock.json b/site/package-lock.json
index 71ff3c1df7..6775b8ee6b 100644
--- a/site/package-lock.json
+++ b/site/package-lock.json
@@ -1423,6 +1423,11 @@
       "integrity": "sha1-G2HAViGQqN/2rjuyzwIAyhMLhtQ=",
       "dev": true
     },
+    "eslint-plugin-svelte3": {
+      "version": "git+https://github.com/sveltejs/eslint-plugin-svelte3.git#d4da8a7d98f2efa70266313ab798cd4d400ca86c",
+      "from": "git+https://github.com/sveltejs/eslint-plugin-svelte3.git",
+      "dev": true
+    },
     "estree-walker": {
       "version": "0.5.2",
       "resolved": "https://registry.npmjs.org/estree-walker/-/estree-walker-0.5.2.tgz",
diff --git a/site/package.json b/site/package.json
index f266d261f8..520e325105 100644
--- a/site/package.json
+++ b/site/package.json
@@ -29,6 +29,7 @@
     "@babel/preset-env": "^7.0.0",
     "@babel/runtime": "^7.0.0",
     "chokidar": "^2.0.4",
+    "eslint-plugin-svelte3": "git+https://github.com/sveltejs/eslint-plugin-svelte3.git",
     "npm-run-all": "^4.1.5",
     "rollup": "^0.68.0",
     "rollup-plugin-babel": "^4.0.2",
diff --git a/site/src/routes/repl/_components/AppControls/index.html b/site/src/routes/repl/_components/AppControls/index.html
index f8aba63c20..b73f98fb81 100644
--- a/site/src/routes/repl/_components/AppControls/index.html
+++ b/site/src/routes/repl/_components/AppControls/index.html
@@ -9,11 +9,10 @@
 
 	const dispatch = createEventDispatcher();
 
+	export let repl;
 	export let examples;
 	export let gist;
 	export let name;
-	export let components;
-	export let json5;
 	export let zen_mode;
 	export let bundle;
 
diff --git a/site/src/routes/repl/_components/CodeMirror.html b/site/src/routes/repl/_components/CodeMirror.html
index 7e05948359..32903fecc6 100644
--- a/site/src/routes/repl/_components/CodeMirror.html
+++ b/site/src/routes/repl/_components/CodeMirror.html
@@ -84,7 +84,7 @@
 	let previous_error_line;
 	$: if (editor) {
 		if (previous_error_line != null) {
-			editor.removeLineClass(previousLine, 'wrap', 'error-line')
+			editor.removeLineClass(previous_error_line, 'wrap', 'error-line')
 		}
 
 		if (error_line && (error_line !== previous_error_line)) {
diff --git a/site/src/routes/repl/_components/Input/ComponentSelector.html b/site/src/routes/repl/_components/Input/ComponentSelector.html
index 9d2057ed01..7eeef3dfbb 100644
--- a/site/src/routes/repl/_components/Input/ComponentSelector.html
+++ b/site/src/routes/repl/_components/Input/ComponentSelector.html
@@ -5,39 +5,29 @@
 
 	const dispatch = createEventDispatcher();
 
-	export let components = [];
-	export let selectedComponent;
+	export let component_store;
+	export let selected_store;
 
 	let editing = null;
 
-	// let previous_components;
-
-	// $: {
-	// 	// bit of a hack...
-	// 	if (components !== previous_components) {
-	// 		selectedComponent = components[0];
-	// 		previous_components = components;
-	// 	}
-	// }
-
-	function selectComponent(component, selectedComponent) {
-		if (selectedComponent != component) {
+	function selectComponent(component) {
+		if ($selected_store != component) {
 			editing = null;
 		}
 
-		dispatch('select', { component });
+		selected_store.set(component);
 	}
 
-	function editTab(component, selectedComponent) {
-		if (selectedComponent === component) {
-			editing = selectedComponent;
+	function editTab(component) {
+		if ($selected_store === component) {
+			editing = $selected_store;
 		}
 	}
 
-	function closeEdit(selectedComponent) {
-		const match = /(.+)\.(html|js)$/.exec(selectedComponent.name);
-		selectedComponent.name = match ? match[1] : selectedComponent.name;
-		if (match && match[2]) selectedComponent.type = match[2];
+	function closeEdit() {
+		const match = /(.+)\.(html|js)$/.exec($selected_store.name);
+		$selected_store.name = match ? match[1] : $selected_store.name;
+		if (match && match[2]) $selected_store.type = match[2];
 		editing = null;
 
 		components = components; // TODO necessary?
@@ -68,11 +58,10 @@
 		setTimeout(() => {
 			// TODO we can do this without IDs
 			document.getElementById(component.name).scrollIntoView(false);
-			// selectedComponent = component;
 		});
 
-		dispatch('create', { component });
-		dispatch('select', { component });
+		component_store.update(components => components.concat(component));
+		selected_store.set(component);
 	}
 </script>
 
@@ -180,12 +169,12 @@
 
 <div class="component-selector">
 	<div class="file-tabs" on:dblclick="{() => dispatch('create')}">
-		{#each components as component}
+		{#each $component_store as component}
 			<button
 				id={component.name}
-				class:active="{component === selectedComponent}"
+				class:active="{component === $selected_store}"
 				data-name={component.name}
-				on:click="{() => selectComponent(component, selectedComponent)}"
+				on:click="{() => selectComponent(component)}"
 				on:dblclick="{e => e.stopPropagation()}"
 			>
 				{#if component.name == 'App'}
@@ -200,14 +189,14 @@
 							autofocus
 							bind:value={component.name}
 							on:focus={selectInput}
-							on:blur="{() => closeEdit(selectedComponent)}"
+							on:blur="{() => closeEdit()}"
 							use:enter="{e => e.target.blur()}"
 						>
 					{:else}
 						<div
 							class="editable"
 							title="edit component name"
-							on:click="{() => editTab(component, selectedComponent)}"
+							on:click="{() => editTab(component)}"
 						>
 							{component.name}.{component.type}
 						</div>
diff --git a/site/src/routes/repl/_components/Input/ModuleEditor.html b/site/src/routes/repl/_components/Input/ModuleEditor.html
index ce38ae6bc6..783dc02dc9 100644
--- a/site/src/routes/repl/_components/Input/ModuleEditor.html
+++ b/site/src/routes/repl/_components/Input/ModuleEditor.html
@@ -27,7 +27,7 @@
 	{#if component}
 		<CodeMirror
 			mode="{component.type === 'js' ? 'javascript' : 'handlebars'}"
-			bind:code={component.source}
+			code={component.source}
 			{error}
 			{errorLoc}
 			{warningCount}
diff --git a/site/src/routes/repl/_components/Input/index.html b/site/src/routes/repl/_components/Input/index.html
index de661c2fc4..50460af098 100644
--- a/site/src/routes/repl/_components/Input/index.html
+++ b/site/src/routes/repl/_components/Input/index.html
@@ -2,27 +2,27 @@
 	import ComponentSelector from './ComponentSelector.html';
 	import ModuleEditor from './ModuleEditor.html';
 
-	export let components;
-	export let selectedComponent;
-	export let sourceError;
-	export let sourceErrorLoc;
-	export let runtimeErrorLoc;
+	export let component_store;
+	export let selected_store;
+
+	export let error;
+	export let errorLoc;
 	export let warningCount;
 </script>
 
 <!-- TODO would be nice if events bubbled -->
 <ComponentSelector
-	{components}
-	bind:selectedComponent
+	{component_store}
+	{selected_store}
 	on:create
 	on:remove
 	on:select
 />
 
 <ModuleEditor
-	component={selectedComponent}
-	error={sourceError}
-	errorLoc="{sourceErrorLoc || runtimeErrorLoc}"
+	component={$selected_store}
+	{error}
+	{errorLoc}
 	{warningCount}
 	on:change
 	on:navigate
diff --git a/site/src/routes/repl/_components/Output/PropEditor.html b/site/src/routes/repl/_components/Output/PropEditor.html
index 0486cf1f34..1839c53627 100644
--- a/site/src/routes/repl/_components/Output/PropEditor.html
+++ b/site/src/routes/repl/_components/Output/PropEditor.html
@@ -6,27 +6,29 @@
 	const dispatch = createEventDispatcher();
 
 	export let value;
-	let json5;
+
+	let error;
+	let code;
 
 	if (value === undefined) {
-		json5 = 'undefined';
+		code = 'undefined';
 	} else {
-		json5 = fleece.stringify(value);
+		code = fleece.stringify(value);
 	}
 
 	$: try {
-		value = fleece.evaluate(json5);
-	} catch (err) {
-		console.error(Object.keys(err));
-		// TODO show in UI
+		value = fleece.evaluate(code);
+	} catch (e) {
+		error = e;
 	}
 
 	function handleChange(event) {
 		try {
 			const value = fleece.evaluate(event.detail.value);
+			error = null;
 			dispatch('change', { value });
-		} catch (err) {
-			// TODO indicate error
+		} catch (e) {
+			error = e;
 		}
 	}
 </script>
@@ -35,21 +37,19 @@
 	.prop-editor {
 		border: 1px solid #eee;
 	}
+
+	.error {
+		background-color: rgba(218, 16, 96, 0.1);
+		border: 1px solid #da106e;
+	}
 </style>
 
-<div class="prop-editor">
+<div class="prop-editor" class:error title="{error && error.message}">
 	<CodeMirror
 		mode="json"
-		bind:code={json5}
+		bind:code
 		lineNumbers={false}
 		on:change={handleChange}
 		flex
 	/>
-</div>
-
-<!-- <CodeMirror
-	mode="json"
-	bind:code={json5}
-	error={dataError}
-	errorLoc={dataErrorLoc}
-/> -->
\ No newline at end of file
+</div>
\ No newline at end of file
diff --git a/site/src/routes/repl/_components/Output/Viewer.html b/site/src/routes/repl/_components/Output/Viewer.html
index 83c58a701b..5a23cc280d 100644
--- a/site/src/routes/repl/_components/Output/Viewer.html
+++ b/site/src/routes/repl/_components/Output/Viewer.html
@@ -8,7 +8,7 @@
 	export let bundle;
 	export let dom;
 	export let ssr;
-	export let values;
+	export let values_store;
 	export let props;
 	export let sourceError;
 	export let error;
@@ -157,7 +157,7 @@
 				const createHtml = () => {
 					try {
 						evalInIframe(`${ssr.code}
-							var rendered = SvelteComponent.render(${JSON.stringify(values)});
+							var rendered = SvelteComponent.render(${JSON.stringify($values_store)});
 
 							if (rendered.css.code) {
 								var style = document.createElement('style');
@@ -190,7 +190,7 @@
 
 							var component = new SvelteComponent({
 								target: document.body,
-								props: ${JSON.stringify(values)}
+								props: ${JSON.stringify($values_store)}
 							});`);
 
 						component = window.app = window.component = iframe.contentWindow.component;
@@ -256,31 +256,7 @@
 				toDestroy = component;
 				component = null;
 
-				if (values !== undefined) init();
-			};
-
-			values_handler = values => {
-				console.log({ values });
-				if (updating) return;
-
-				try {
-					if (component) {
-						error = null;
-						updating = true;
-						component.$set(values);
-						updating = false;
-					} else {
-						init();
-					}
-				} catch (e) {
-					const loc = getLocationFromStack(e.stack, bundle.map);
-					if (loc) {
-						e.filename = loc.source;
-						e.loc = { line: loc.line, column: loc.column };
-					}
-
-					error = e;
-				}
+				init();
 			};
 
 			props_handler = props => {
@@ -296,6 +272,9 @@
 					// (answer: probably)
 					component.$$.bound[prop] = value => {
 						dispatch('binding', { prop, value });
+						values_store.update(values => Object.assign({}, values, {
+							[prop]: value
+						}));
 					};
 				});
 			};
@@ -305,12 +284,15 @@
 	function noop(){}
 	let run = noop;
 	let bundle_handler = noop;
-	let values_handler = noop;
 	let props_handler = noop;
 
 	$: bundle_handler(bundle);
-	$: values_handler(values);
 	$: props_handler(props);
+
+	// pending https://github.com/sveltejs/svelte/issues/1889
+	$: {
+		$values_store;
+	}
 </script>
 
 <style>
diff --git a/site/src/routes/repl/_components/Output/index.html b/site/src/routes/repl/_components/Output/index.html
index 725342bc56..d9c2b59fcb 100644
--- a/site/src/routes/repl/_components/Output/index.html
+++ b/site/src/routes/repl/_components/Output/index.html
@@ -5,16 +5,14 @@
 	import CodeMirror from '../CodeMirror.html';
 
 	export let bundle
-	export let compiled;
+	export let code;
 	export let dom;
 	export let ssr;
 	export let props;
-	export let values;
+	export let values_store;
 	export let json5;
 	export let sourceError;
 	export let runtimeError;
-	export let dataError;
-	export let dataErrorLoc;
 
 	// refs
 	let viewer;
@@ -22,14 +20,20 @@
 
 	let view = 'result';
 
+	function updateValues(prop, value) {
+		values_store.update(v => Object.assign({}, v, {
+			[prop]: value
+		}));
+	}
+
 	function setPropFromViewer(prop, value) {
-		// console.log(`setting prop from component`, prop, value);
 		// propEditors[prop].setValue(value);
+		updateValues(prop, value);
 	}
 
 	function setPropFromEditor(prop, value) {
-		console.log(`setting prop from editor`, prop, value);
 		viewer.setProp(prop, value);
+		updateValues(prop, value);
 	}
 </script>
 
@@ -75,8 +79,8 @@
 		display: grid;
 		padding: 0.5em;
 		grid-template-columns: auto 1fr;
-		grid-template-rows: min-content;
-		grid-column-gap: 0.5em;
+		grid-auto-rows: min-content;
+		grid-gap: 0.5em;
 		overflow-y: auto;
 	}
 
@@ -107,8 +111,7 @@
 					{bundle}
 					{dom}
 					{ssr}
-					{data}
-					bind:values
+					{values_store}
 					{props}
 					{sourceError}
 					bind:error={runtimeError}
@@ -125,17 +128,27 @@
 		<section slot="b">
 			<h3>Props editor</h3>
 
-			<div class="props">
-				{#each props.sort() as prop (prop)}
-					<code style="display: block; whitespace: pre;">{prop}</code>
-
-					<!-- TODO `bind:this={propEditors[prop]}` — currently fails -->
-					<PropEditor
-						value={values[prop]}
-						on:change="{e => setPropFromEditor(prop, e.detail.value)}"
-					/>
-				{/each}
-			</div>
+			{#if props}
+				{#if props.length > 0}
+					<div class="props">
+						{#each props.sort() as prop (prop)}
+							<code style="display: block; whitespace: pre;">{prop}</code>
+
+							<!-- TODO `bind:this={propEditors[prop]}` — currently fails -->
+							<PropEditor
+								value={$values_store[prop]}
+								on:change="{e => setPropFromEditor(prop, e.detail.value)}"
+							/>
+						{/each}
+					</div>
+				{:else}
+					<div style="padding: 0.5em">
+						<!-- TODO explain distincion between logic-less and logic-ful components? -->
+						<!-- TODO style the <a> so it looks like a link -->
+						<p>This component has no props — <a href="guide#external-properties">declare props with the export keyword</a></p>
+					</div>
+				{/if}
+			{/if}
 		</section>
 	</SplitPane>
 {:else}
@@ -143,7 +156,7 @@
 		<div slot="a">
 			<CodeMirror
 				mode="javascript"
-				code={compiled}
+				{code}
 				error={sourceError}
 				errorLoc={sourceErrorLoc}
 				readonly
diff --git a/site/src/routes/repl/_components/Repl.html b/site/src/routes/repl/_components/Repl.html
index c69dfd17c9..c36cb195da 100644
--- a/site/src/routes/repl/_components/Repl.html
+++ b/site/src/routes/repl/_components/Repl.html
@@ -1,5 +1,6 @@
 <script>
 	import { onMount } from 'svelte';
+	import { writable } from 'svelte/store';
 	import * as fleece from 'golden-fleece';
 	import SplitPane from './SplitPane.html';
 	import CodeMirror from './CodeMirror.html';
@@ -7,151 +8,146 @@
 	import Output from './Output/index.html';
 
 	export let version;
-	export let components;
-	export let selectedComponent;
-	export let values;
+	export let app;
+
+	let component_store = writable([]);
+	let values_store = writable({});
+	let selected_store = writable(null);
+
+	$: {
+		component_store.set(app.components);
+		values_store.set(app.values);
+		selected_store.set(app.components[0]);
+	}
+
+	$: {
+		// necessary pending https://github.com/sveltejs/svelte/issues/1889
+		$component_store;
+	}
+
+	let workers;
 
 	let bundle = null;
 	let dom;
 	let ssr;
 	let sourceError = null;
 	let runtimeError = null;
-	let dataError = null;
-	let dataErrorLoc = null;
 	let warningCount = 0;
 	let code = '';
 	let uid = 0;
-	let props = [];
+	let props = null;
 	let sourceErrorLoc;
 	let runtimeErrorLoc;
 
-	let worker;
-
 	onMount(async () => {
-		worker = new Worker('/repl-worker.js');
-
-		function listener(event) {
-			switch (event.data.type) {
-				case 'version':
-					version = event.data.version;
-					break;
-
-				case 'bundled':
-					({ bundle, dom, ssr, warningCount, error: sourceError } = event.data.result);
-					console.log(dom, sourceError);
-					runtimeError = null;
-					break;
-
-				case 'compiled':
-					code = event.data.result.code;
-					if (event.data.result.props) props = event.data.result.props;
-					break;
-			}
-		}
+		workers = {
+			compiler: new Worker('/workers/compiler.js'),
+			bundler: new Worker('/workers/bundler.js')
+		};
 
-		worker.addEventListener('message', listener);
+		workers.compiler.postMessage({ type: 'init', version });
+		workers.compiler.onmessage = event => {
+			code = event.data.code;
+			if (event.data.props) props = event.data.props;
+		};
 
-		worker.postMessage({ type: 'init', version });
+		workers.bundler.postMessage({ type: 'init', version });
+		workers.bundler.onmessage = event => {
+			({ bundle, dom, ssr, warningCount, error: sourceError } = event.data);
+			if (sourceError) console.error(sourceError);
+			runtimeError = null;
+		};
 
 		return () => {
-			worker.removeEventListener('message', listener);
-			worker.terminate();
+			workers.compiler.terminate();
+			workers.bundler.terminate();
 		};
 	});
 
 	function removeComponent() {
-		const component = selectedComponent;
+		const selected = $selected_store;
 
-		if (component.name === 'App') {
+		if (selected.name === 'App') {
 			// App.html can't be removed
-			component.source = '';
-			selectedComponent = component;
+			selected.source = '';
+			// $selected_store.set(selected);
 		} else {
-			const index = components.indexOf(component);
+			const components = $component_store;
+			const index = components.indexOf(selected);
+
 			if (~index) {
-				components = components.slice(0, index).concat(components.slice(index + 1));
+				component_store.set(components.slice(0, index).concat(components.slice(index + 1)));
 			} else {
 				console.error(`Could not find component! That's... odd`);
 			}
 
-			selectedComponent = components[index] || components[components.length - 1];
+			selected_store.set(components[index] || components[components.length - 1]);
 		}
 	}
 
 	function compile(component) {
 		if (component.type === 'html') {
-			worker.postMessage({
+			workers.compiler.postMessage({
 				type: 'compile',
-				component,
-				entry: component === components[0]
+				source: component.source,
+				options: {
+					name: component.name,
+					filename: `${component.name}.html`
+				},
+				entry: component === $component_store[0]
 			});
 		} else {
 			code = component.source;
 		}
 	}
 
-	function handleSelect(event) {
-		console.log(`handleSelect`);
-
-		selectedComponent = event.detail.component;
-		// compile(selectedComponent);
-	}
+	function handleChange(event) {
+		selected_store.update(component => {
+			// TODO this is a bit hacky — we're relying on mutability
+			// so that updating component_store works... might be better
+			// if a) components had unique IDs, b) we tracked selected
+			// *index* rather than component, and c) `selected` was
+			// derived from `components` and `index`
+			component.source = event.detail.value;
+			return component;
+		});
 
-	function handleChange() {
-		console.log(`handleChange`);
+		component_store.update(c => c);
 
 		// recompile selected component
-		compile(selectedComponent);
+		compile($selected_store);
 
 		// regenerate bundle (TODO do this in a separate worker?)
-		worker.postMessage({ type: 'bundle', components });
-	}
-
-	function updateData(current) {
-		const data = fleece.evaluate(json5);
-
-		for (const key in data) {
-			data[key] = current[key];
-		}
-
-		json5 = fleece.patch(json5, data);
+		workers.bundler.postMessage({ type: 'bundle', components: $component_store });
 	}
 
 	function navigate(filename) {
 		const name = filename.replace(/\.html$/, '');
 
-		if (selectedComponent.name === name) return;
-		selectedComponent = components.find(c => c.name === name);
+		console.error(`TODO navigate`);
+
+		// if (selected.name === name) return;
+		// selected = components.find(c => c.name === name);
 	}
 
-	$: if (sourceError && selectedComponent) {
-		sourceErrorLoc = sourceError.filename === `${selectedComponent.name}.${selectedComponent.type}`
+	$: if (sourceError && $selected_store) {
+		sourceErrorLoc = sourceError.filename === `${$selected_store.name}.${$selected_store.type}`
 			? sourceError.start
 			: null;
 	}
 
-	$: if (runtimeError && selectedComponent) {
-		runtimeErrorLoc = runtimeError.filename === `${selectedComponent.name}.${selectedComponent.type}`
+	$: if (runtimeError && $selected_store) {
+		runtimeErrorLoc = runtimeError.filename === `${$selected_store.name}.${$selected_store.type}`
 			? runtimeError.start
 			: null;
 	}
 
-	$: if (worker && components) {
-		console.log(`posting`, worker, components);
-		worker.postMessage({ type: 'bundle', components });
-	}
-
-	$: if (worker && selectedComponent) {
-		compile(selectedComponent);
+	$: if (workers && app.components) {
+		workers.bundler.postMessage({ type: 'bundle', components: app.components });
 	}
 
-	$: try {
-		data= fleece.evaluate(json5);
-		dataError = null;
-		dataErrorLoc = null;
-	} catch (err) {
-		dataError = err;
-		dataErrorLoc = err && err.loc;
+	$: if (workers && $selected_store) {
+		compile($selected_store);
 	}
 </script>
 
@@ -239,13 +235,12 @@
 	<SplitPane type="horizontal">
 		<section slot=a>
 			<Input
-				bind:components
-				{selectedComponent}
+				{component_store}
+				{selected_store}
+				{values_store}
 				error={sourceError}
 				errorLoc="{sourceErrorLoc || runtimeErrorLoc}"
 				{warningCount}
-				on:create="{e => components = components.concat(e.detail.component)}"
-				on:select="{e => selectedComponent = e.detail.component}"
 				on:remove={removeComponent}
 				on:change="{handleChange}"
 			/>
@@ -253,16 +248,16 @@
 
 		<section slot=b style='height: 100%;'>
 			<Output
+				{version}
+				{selected_store}
 				{code}
 				{bundle}
 				{ssr}
 				{dom}
 				{props}
-				{values}
+				{values_store}
 				{sourceError}
 				{runtimeError}
-				{dataError}
-				{dataErrorLoc}
 			/>
 		</section>
 	</SplitPane>
diff --git a/site/src/routes/repl/index.html b/site/src/routes/repl/index.html
index 70db545558..9c38bc4e96 100644
--- a/site/src/routes/repl/index.html
+++ b/site/src/routes/repl/index.html
@@ -8,19 +8,26 @@
 
 	export let query;
 
-	let version = query.version || 'alpha';
-	let components;
-	let selectedComponent;
-	let values = {};
+	let version = query.version;
+	let demo = query.demo || 'hello-world';
+	let gist = query.gist;
+
+	let app = {
+		components: [],
+		values: {}
+	};
+
 	let name = 'loading...';
 	let zen_mode = false;
 
+	let repl;
+
 	$: if (typeof history !== 'undefined') {
 		const params = [];
 
 		if (version !== 'latest') params.push(`version=${version}`);
-		if (query.gist) params.push(`gist=${query.gist}`);
-		else if (query.demo) params.push(`demo=${query.demo}`);
+		if (gist) params.push(`gist=${gist}`);
+		else if (demo) params.push(`demo=${demo}`);
 
 		const url = params.length > 0
 			? `repl?${params.join('&')}`
@@ -37,17 +44,24 @@
 	});
 
 	onMount(() => {
-		if (query.gist) {
-			fetch(`gist/${query.gist}`).then(r => r.json()).then(gist => {
-				name = gist.description;
-				values = {};
+		fetch(`https://unpkg.com/svelte@${version || 'alpha'}/package.json`)
+			.then(r => r.json())
+			.then(pkg => {
+				version = pkg.version;
+			});
 
-				components = Object.keys(gist.files)
+		if (gist) {
+			fetch(`gist/${gist}`).then(r => r.json()).then(({ description, files }) => {
+				name = description;
+
+				const values = {};
+
+				const components = Object.keys(files)
 					.map(file => {
 						const dot = file.lastIndexOf('.');
 						if (!~dot) return;
 
-						const source = gist.files[file].content;
+						const source = files[file].content;
 
 						// while we're here...
 						if (file === 'data.json' || file === 'data.json5') {
@@ -70,27 +84,26 @@
 						return a.name < b.name ? -1 : 1;
 					});
 
-				selectedComponent = components[0];
+				app = { components, values };
 			});
-		} else if (!query.demo) {
-			query.demo = 'hello-world';
 		}
 	});
 
 	function load_demo(slug) {
-		const url = slugs.has(query.demo)
-			? `api/examples/${query.demo}`
-			: `guide/demo/${query.demo}.json`;
+		const url = slugs.has(slug)
+			? `api/examples/${slug}`
+			: `guide/demo/${slug}.json`;
 
 		fetch(url).then(async response => {
 			if (response.ok) {
-				const demo = await response.json();
+				const data = await response.json();
 
-				name = demo.title;
-				values = tryParseData(demo.json5) || {}; // TODO make this more error-resistant
-				components = demo.components;
+				name = data.title;
 
-				selectedComponent = components[0];
+				app = {
+					values: tryParseData(data.json5) || {}, // TODO make this more error-resistant
+					components: data.components
+				};
 			}
 		});
 	}
@@ -103,8 +116,8 @@
 		}
 	}
 
-	$: if (process.browser && query.demo) {
-		load_demo(query.demo);
+	$: if (process.browser && demo) {
+		load_demo(demo);
 	}
 </script>
 
@@ -171,19 +184,16 @@
 <div class="repl-outer {zen_mode ? 'zen-mode' : ''}">
 	<AppControls
 		{examples}
-		{components}
-		{values}
+		{app}
 		{name}
-		gist_id={query.gist}
+		{gist}
+		{repl}
 		bind:zen_mode
-		on:select="{e => query = Object.assign({}, query, { demo: e.detail.slug, gist: null })}"
-		on:forked="{e => query = Object.assign({}, query, { demo: null, gist: e.detail.gist })}"
+		on:select="{e => (demo = e.detail.slug, gist = null)}"
+		on:forked="{e => (demo = null, gist = e.detail.gist)}"
 	/>
 
-	<Repl
-		bind:version
-		{components}
-		{selectedComponent}
-		{values}
-	/>
+	{#if process.browser}
+		<Repl bind:this={repl} {version} {app}/>
+	{/if}
 </div>
diff --git a/site/static/repl-worker.js b/site/static/workers/bundler.js
similarity index 75%
rename from site/static/repl-worker.js
rename to site/static/workers/bundler.js
index e0627af393..41ecdbd0c1 100644
--- a/site/static/repl-worker.js
+++ b/site/static/workers/bundler.js
@@ -1,59 +1,39 @@
 self.window = self; // egregious hack to get magic-string to work in a worker
 
 let version;
-let fulfil_ready;
-const ready = new Promise(f => {
-	fulfil_ready = f;
-});
+
+let fulfil;
+let ready = new Promise(f => fulfil = f);
 
 self.addEventListener('message', async event => {
 	switch (event.data.type) {
 		case 'init':
-			version = await init(event.data.version);
-			postMessage({
-				type: 'version',
-				version
-			});
+			version = event.data.version;
+
+			importScripts(
+				`https://unpkg.com/svelte@${version}/compiler.js`,
+				`https://unpkg.com/rollup/dist/rollup.browser.js`
+			);
+			fulfil();
+
 			break;
 
 		case 'bundle':
-			await ready;
-			postMessage({
-				type: 'bundled',
-				result: await bundle(event.data.components)
-			});
-			break;
+			if (event.data.components.length === 0) return;
 
-		case 'compile':
 			await ready;
-			postMessage({
-				type: 'compiled',
-				result: compile(event.data.component, event.data.entry)
-			});
-			break;
+			postMessage(
+				await bundle(event.data.components)
+			);
 
+			break;
 	}
 });
 
 const commonCompilerOptions = {
-	cascade: false,
-	store: true,
-	skipIntroByDefault: true,
-	nestedTransitions: true,
 	dev: true,
 };
 
-async function init(version) {
-	// TODO use local versions
-	importScripts(
-		`https://unpkg.com/svelte@${version}/compiler.js`,
-		`https://unpkg.com/rollup/dist/rollup.browser.js`
-	);
-
-	fulfil_ready();
-	return version === 'local' ? version : svelte.VERSION;
-}
-
 let cached = {
 	dom: null,
 	ssr: null
@@ -107,7 +87,6 @@ async function getBundle(mode, cache, lookup) {
 				},
 				load(id) {
 					if (id.startsWith(`https://`)) return fetch_if_uncached(id);
-
 					if (id in lookup) return lookup[id].source;
 				},
 				transform(code, id) {
@@ -231,21 +210,4 @@ async function bundle(components) {
 			})
 		};
 	}
-}
-
-function compile(component, entry) {
-	try {
-		const { js, stats } = svelte.compile(component.source, Object.assign({
-			// TODO make options configurable
-			name: component.name,
-			filename: component.name + '.html',
-		}, commonCompilerOptions));
-
-		return { code: js.code, props: entry ? stats.props : null };
-	} catch (err) {
-		let result = `/* Error compiling component\n\n${err.message}`;
-		if (err.frame) result += `\n${err.frame}`;
-		result += `\n\n*/`;
-		return { code: result, props: null };
-	}
-}
+}
\ No newline at end of file
diff --git a/site/static/workers/compiler.js b/site/static/workers/compiler.js
new file mode 100644
index 0000000000..7759c492a3
--- /dev/null
+++ b/site/static/workers/compiler.js
@@ -0,0 +1,41 @@
+self.window = self; // egregious hack to get magic-string to work in a worker
+
+let fulfil_ready;
+const ready = new Promise(f => {
+	fulfil_ready = f;
+});
+
+self.addEventListener('message', async event => {
+	switch (event.data.type) {
+		case 'init':
+			importScripts(`https://unpkg.com/svelte@${event.data.version}/compiler.js`);
+			fulfil_ready();
+			break;
+
+		case 'compile':
+			await ready;
+			postMessage(compile(event.data));
+			break;
+
+	}
+});
+
+const commonCompilerOptions = {
+	dev: false
+};
+
+function compile({ source, options, entry }) {
+	try {
+		const { js, stats } = svelte.compile(
+			source,
+			Object.assign({}, commonCompilerOptions, options)
+		);
+
+		return { code: js.code, props: entry ? stats.props : null };
+	} 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 };
+	}
+}