[IMP] component: validate mounting target at patch time

src/app/app.ts

@@ -4,6 +4,7 @@ import { MountOptions } from "../component/fibers";
 import { Scheduler } from "../component/scheduler";
 import { TemplateSet, TemplateSetConfig } from "./template_set";
 import { nodeErrorHandlers } from "../component/error_handling";
+import { validateTarget } from "../utils";
 
 // reimplement dev mode stuff see last change in 0f7a8289a6fb8387c3c1af41c6664b2a8448758f
 
@@ -48,22 +49,13 @@ export class App<
   }
 
   mount(target: HTMLElement, options?: MountOptions): Promise<Component<P, E> & InstanceType<T>> {
-    this.checkTarget(target);
+    validateTarget(target);
     const node = this.makeNode(this.Root, this.props);
     const prom = this.mountNode(node, target, options);
     this.root = node;
     return prom;
   }
 
-  checkTarget(target: HTMLElement) {
-    if (!(target instanceof HTMLElement)) {
-      throw new Error("Cannot mount component: the target is not a valid DOM element");
-    }
-    if (!document.body.contains(target)) {
-      throw new Error("Cannot mount a component on a detached dom node");
-    }
-  }
-
   makeNode(Component: ComponentConstructor, props: any): ComponentNode {
     return new ComponentNode(Component, props, this);
   }

src/component/fibers.ts

@@ -1,4 +1,5 @@
 import { BDom, mount } from "../blockdom";
+import { validateTarget } from "../utils";
 import type { ComponentNode } from "./component_node";
 import { fibersInError, handleError } from "./error_handling";
 import { STATUS } from "./status";
@@ -158,6 +159,7 @@ export class MountFiber extends RootFiber {
   complete() {
     let current: Fiber | undefined = this;
     try {
+      validateTarget(this.target);
       const node = this.node;
       if (node.bdom) {
         // this is a complicated situation: if we mount a fiber with an existing

src/utils.ts

@@ -24,6 +24,15 @@ export function batched(callback: Callback): Callback {
   };
 }
 
+export function validateTarget(target: HTMLElement) {
+  if (!(target instanceof HTMLElement)) {
+    throw new Error("Cannot mount component: the target is not a valid DOM element");
+  }
+  if (!document.body.contains(target)) {
+    throw new Error("Cannot mount a component on a detached dom node");
+  }
+}
+
 export class EventBus extends EventTarget {
   trigger(name: string, payload?: any) {
     this.dispatchEvent(new CustomEvent(name, { detail: payload }));

tests/components/__snapshots__/basics.test.ts.snap

@@ -81,6 +81,19 @@ exports[`basics a class component inside a class component, no external dom 2`]
 }"
 `;
 
+exports[`basics a component cannot be mounted in a detached node (even if node is detached later 1`] = `
+"function anonymous(bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, component, comment } = bdom;
+  
+  let block1 = createBlock(\`<div/>\`);
+  
+  return function template(ctx, node, key = \\"\\") {
+    return block1();
+  }
+}"
+`;
+
 exports[`basics a component inside a component 1`] = `
 "function anonymous(bdom, helpers
 ) {

tests/components/basics.test.ts

@@ -171,6 +171,27 @@ describe("basics", () => {
     expect(error!.message).toBe("Cannot mount a component on a detached dom node");
   });
 
+  test("a component cannot be mounted in a detached node (even if node is detached later)", async () => {
+    const warn = console.warn;
+    console.warn = jest.fn();
+    class Test extends Component {
+      static template = xml`<div/>`;
+    }
+    let error: Error;
+    const prom = mount(Test, fixture);
+    await Promise.resolve();
+    fixture.remove();
+    try {
+      await prom;
+    } catch (e) {
+      error = e as Error;
+    }
+    expect(error!).toBeDefined();
+    expect(error!.message).toBe("Cannot mount a component on a detached dom node");
+    expect(console.warn).toBeCalledTimes(1);
+    console.warn = warn;
+  });
+
   test("crashes if it cannot find a template", async () => {
     class Test extends Component {
       static template = "wrongtemplate";