Initial draft for error handling using `onError`

src/compiler/compile/render_dom/Block.ts

@@ -461,6 +461,10 @@ export default class Block {
 
 			this.add_variable(dispose);
 
+            this.event_listeners.forEach(event_listener => {
+                event_listener.arguments[2] = x`@attach_error_handler.call(${event_listener.arguments[0]}, #component, ${event_listener.arguments[2]})`;
+            });
+
 			if (this.event_listeners.length === 1) {
 				this.chunks.mount.push(
 					b`

src/compiler/compile/render_dom/index.ts

@@ -329,7 +329,7 @@ export default function dom(
 	const has_create_fragment = component.compile_options.dev || block.has_content();
 	if (has_create_fragment) {
 		body.push(b`
-			function create_fragment(#ctx) {
+			function create_fragment(#ctx, #component) {
 				${block.get_contents()}
 			}
 		`);
@@ -450,6 +450,15 @@ export default function dom(
 			}) as Expression)
 		};
 
+        const instance_try_block: any = b`
+            try {}
+            catch(e) {
+                @handle_error($$self, e);
+            }
+        `;
+
+        instance_try_block[0].block.body = instance_javascript.flat();
+
 		body.push(b`
 			function ${definition}(${args}) {
 				${injected.map(name => b`let ${name};`)}
@@ -466,7 +475,7 @@ export default function dom(
 				${component.compile_options.dev && b`@validate_slots('${component.tag}', #slots, [${[...component.slots.keys()].map(key => `'${key}'`).join(',')}]);`}
 				${compute_slots}
 
-				${instance_javascript}
+				${instance_try_block}
 
 				${unknown_props_check}
 

src/runtime/index.ts

@@ -3,6 +3,7 @@ import './ambient';
 export {
 	onMount,
 	onDestroy,
+    onError,
 	beforeUpdate,
 	afterUpdate,
 	setContext,

src/runtime/internal/Component.ts

@@ -36,6 +36,7 @@ interface T$$ {
 	context: Map<any, any>;
 	on_mount: any[];
 	on_destroy: any[];
+    on_error: any[];
 	skip_bound: boolean;
 	on_disconnect: any[];
 	root:Element|ShadowRoot
@@ -104,6 +105,26 @@ function make_dirty(component, i) {
 	component.$$.dirty[(i / 31) | 0] |= (1 << (i % 31));
 }
 
+export function attach_error_handler(component, fn) {
+    return () => {
+        try {
+            fn.call(this, ...arguments);
+        } catch (e) {
+            handle_error(component, e);
+        }
+    }
+}
+
+export function handle_error(component, e) {
+    if (component.$$.on_error.length === 0) {
+        throw e;
+    }
+
+    component.$$.on_error.forEach(handler => {
+        handler(e);
+    });
+}
+
 export function init(component, options, instance, create_fragment, not_equal, props, append_styles, dirty = [-1]) {
 	const parent_component = current_component;
 	set_current_component(component);
@@ -122,6 +143,7 @@ export function init(component, options, instance, create_fragment, not_equal, p
 		on_mount: [],
 		on_destroy: [],
 		on_disconnect: [],
+        on_error: [],
 		before_update: [],
 		after_update: [],
 		context: new Map(parent_component ? parent_component.$$.context : options.context || []),
@@ -153,7 +175,7 @@ export function init(component, options, instance, create_fragment, not_equal, p
 	run_all($$.before_update);
 
 	// `false` as a special case of no DOM component
-	$$.fragment = create_fragment ? create_fragment($$.ctx) : false;
+	$$.fragment = create_fragment ? create_fragment($$.ctx, component) : false;
 
 	if (options.target) {
 		if (options.hydrate) {

src/runtime/internal/lifecycle.ts

@@ -27,6 +27,10 @@ export function onDestroy(fn: () => any) {
 	get_current_component().$$.on_destroy.push(fn);
 }
 
+export function onError(fn: () => any) {
+    get_current_component().$$.on_error.push(fn);
+}
+
 export function createEventDispatcher<
 	EventMap extends {} = any
 >(): <EventKey extends Extract<keyof EventMap, string>>(type: EventKey, detail?: EventMap[EventKey]) => void {