fix binding groups

src/compile/render-dom/index.ts

@@ -274,6 +274,10 @@ export default function dom(
 		filtered_declarations.push(...arr.map(name => `$$slot_${sanitize(name)}`), '$$scope');
 	}
 
+	if (renderer.bindingGroups.length > 0) {
+		filtered_declarations.push(`$$binding_groups`);
+	}
+
 	const has_definition = (
 		component.javascript ||
 		filtered_props.length > 0 ||
@@ -313,6 +317,8 @@ export default function dom(
 
 				${renderer.slots.size && `let { ${[...renderer.slots].map(name => `$$slot_${sanitize(name)}`).join(', ')}, $$scope } = $$props;`}
 
+				${renderer.bindingGroups.length > 0 && `const $$binding_groups = [${renderer.bindingGroups.map(_ => `[]`).join(', ')}];`}
+
 				${component.partly_hoisted.length > 0 && component.partly_hoisted.join('\n\n')}
 
 				${reactive_store_subscriptions}

src/compile/render-dom/wrappers/Element/Binding.ts

@@ -124,7 +124,7 @@ export default class BindingWrapper {
 				const bindingGroup = getBindingGroup(parent.renderer, this.node.expression.node);
 
 				block.builders.hydrate.addLine(
-					`(ctx.$$binding_groups[${bindingGroup}] || (ctx.$$binding_groups[${bindingGroup}] = [])).push(${parent.var});`
+					`ctx.$$binding_groups[${bindingGroup}].push(${parent.var});`
 				);
 
 				block.builders.destroy.addLine(
@@ -278,7 +278,7 @@ function getValueFromDom(
 	if (name === 'group') {
 		const bindingGroup = getBindingGroup(renderer, binding.node.expression.node);
 		if (type === 'checkbox') {
-			return `@getBindingGroupValue($$self.ctx.$$binding_groups[${bindingGroup}])`;
+			return `@getBindingGroupValue($$binding_groups[${bindingGroup}])`;
 		}
 
 		return `this.__value`;

src/internal/Component.js

@@ -98,8 +98,6 @@ export function init(component, options, instance, create_fragment, not_equal) {
 		})
 		: props;
 
-	$$.ctx.$$binding_groups = []; // TODO this is awkward and usually unncessary
-
 	$$.update();
 	ready = true;
 	run_all($$.before_render);