improve validation

src/compiler/compile/render_dom/wrappers/InlineComponent/index.ts

@@ -416,8 +416,7 @@ export default class InlineComponentWrapper extends Wrapper {
 				}
 
 				if (${switch_value}) {
-					${component.compile_options.dev && b`@validate_svelte_component(${switch_value});`}
-					${name} = new ${switch_value}(${switch_props}(#ctx));
+					${name} = @construct_svelte_component(${switch_value}, ${switch_props}(#ctx));
 
 					${munged_bindings}
 					${munged_handlers}
@@ -461,8 +460,7 @@ export default class InlineComponentWrapper extends Wrapper {
 					}
 
 					if (${switch_value}) {
-						${component.compile_options.dev && b`@validate_svelte_component(${switch_value});`}
-						${name} = new ${switch_value}(${switch_props}(#ctx));
+						${name} = @construct_svelte_component(${switch_value}, ${switch_props}(#ctx));
 
 						${munged_bindings}
 						${munged_handlers}

src/runtime/internal/dev.ts

@@ -121,9 +121,21 @@ export function validate_void_dynamic_element(tag: undefined | string) {
 	}
 }
 
-export function validate_svelte_component(component: any) {
-	if (!(component.prototype instanceof SvelteComponent)) {
-		throw new Error('this={...} of <svelte:component> should specify a Svelte component.');
+export function construct_svelte_component_dev(component, props) {
+	const error_message = 'this={...} of <svelte:component> should specify a Svelte component.';
+	try {
+		const instance = new component(props);
+		if (!instance.$$ || !instance.$set || !instance.$on || !instance.$destroy) {
+			throw new Error(error_message);
+		}
+		return instance;
+	} catch (err) {
+		const { message } = err;
+		if (typeof message === 'string' && message.indexOf('is not a constructor') !== -1) {
+			throw new Error(error_message);
+		} else {
+			throw err;
+		}
 	}
 }
 

src/runtime/internal/dom.ts

@@ -740,3 +740,7 @@ export function get_custom_elements_slots(element: HTMLElement) {
 	});
 	return result;
 }
+
+export function construct_svelte_component(component, props) {
+	return new component(props);
+}