feat: implement Element.waitForSelector (#7825)

Co-authored-by: Johan Bay <jobay@google.com>
Co-authored-by: Mathias Bynens <mathias@qiwi.be>

docs/api.md

@@ -336,6 +336,7 @@
   * [elementHandle.toString()](#elementhandletostring)
   * [elementHandle.type(text[, options])](#elementhandletypetext-options)
   * [elementHandle.uploadFile(...filePaths)](#elementhandleuploadfilefilepaths)
+  * [elementHandle.waitForSelector(selector[, options])](#elementhandlewaitforselectorselector-options)
 - [class: HTTPRequest](#class-httprequest)
   * [httpRequest.abort([errorCode], [priority])](#httprequestaborterrorcode-priority)
   * [httpRequest.abortErrorReason()](#httprequestaborterrorreason)
@@ -4872,6 +4873,19 @@ await elementHandle.press('Enter');
 
 This method expects `elementHandle` to point to an [input element](https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input).
 
+#### elementHandle.waitForSelector(selector[, options])
+
+- `selector` <[string]> A [selector] of an element to wait for
+- `options` <[Object]> Optional waiting parameters
+  - `visible` <[boolean]> wait for element to be present in DOM and to be visible, i.e. to not have `display: none` or `visibility: hidden` CSS properties. Defaults to `false`.
+  - `hidden` <[boolean]> wait for element to not be found in the DOM or to be hidden, i.e. have `display: none` or `visibility: hidden` CSS properties. Defaults to `false`.
+  - `timeout` <[number]> maximum time to wait for in milliseconds. Defaults to `30000` (30 seconds). Pass `0` to disable timeout. The default value can be changed by using the [page.setDefaultTimeout(timeout)](#pagesetdefaulttimeouttimeout) method.
+- returns: <[Promise]<?[ElementHandle]>> Promise which resolves when element specified by selector string is added to DOM. Resolves to `null` if waiting for `hidden: true` and selector is not found in DOM.
+
+Wait for an element matching `selector` to appear within the `elementHandle`’s subtree. If the `selector` already matches an element at the moment of calling the method, the promise returned by the method resolves immediately. If the selector doesn’t appear after `timeout` milliseconds of waiting, the promise rejects.
+
+This method does not work across navigations or if the element is detached from DOM.
+
 ### class: HTTPRequest
 
 Whenever the page sends a request, such as for a network resource, the following events are emitted by Puppeteer's page:

src/common/DOMWorld.ts

@@ -58,6 +58,7 @@ export interface WaitForSelectorOptions {
   visible?: boolean;
   hidden?: boolean;
   timeout?: number;
+  root?: ElementHandle;
 }
 
 /**
@@ -631,13 +632,14 @@ export class DOMWorld {
       waitForHidden ? ' to be hidden' : ''
     }`;
     async function predicate(
+      root: Element | Document,
       selector: string,
       waitForVisible: boolean,
       waitForHidden: boolean
     ): Promise<Node | null | boolean> {
       const node = predicateQueryHandler
-        ? ((await predicateQueryHandler(document, selector)) as Element)
-        : document.querySelector(selector);
+        ? ((await predicateQueryHandler(root, selector)) as Element)
+        : root.querySelector(selector);
       return checkWaitForOptions(node, waitForVisible, waitForHidden);
     }
     const waitTaskOptions: WaitTaskOptions = {
@@ -648,6 +650,7 @@ export class DOMWorld {
       timeout,
       args: [selector, waitForVisible, waitForHidden],
       binding,
+      root: options.root,
     };
     const waitTask = new WaitTask(waitTaskOptions);
     const jsHandle = await waitTask.promise;
@@ -671,13 +674,14 @@ export class DOMWorld {
     const polling = waitForVisible || waitForHidden ? 'raf' : 'mutation';
     const title = `XPath \`${xpath}\`${waitForHidden ? ' to be hidden' : ''}`;
     function predicate(
+      root: Element | Document,
       xpath: string,
       waitForVisible: boolean,
       waitForHidden: boolean
     ): Node | null | boolean {
       const node = document.evaluate(
         xpath,
-        document,
+        root,
         null,
         XPathResult.FIRST_ORDERED_NODE_TYPE,
         null
@@ -691,6 +695,7 @@ export class DOMWorld {
       polling,
       timeout,
       args: [xpath, waitForVisible, waitForHidden],
+      root: options.root,
     };
     const waitTask = new WaitTask(waitTaskOptions);
     const jsHandle = await waitTask.promise;
@@ -737,6 +742,7 @@ export interface WaitTaskOptions {
   timeout: number;
   binding?: PageBinding;
   args: SerializableOrJSHandle[];
+  root?: ElementHandle;
 }
 
 /**
@@ -755,6 +761,7 @@ export class WaitTask {
   _reject: (x: Error) => void;
   _timeoutTimer?: NodeJS.Timeout;
   _terminated = false;
+  _root: ElementHandle;
 
   constructor(options: WaitTaskOptions) {
     if (helper.isString(options.polling))
@@ -777,6 +784,7 @@ export class WaitTask {
     this._domWorld = options.domWorld;
     this._polling = options.polling;
     this._timeout = options.timeout;
+    this._root = options.root;
     this._predicateBody = getPredicateBody(options.predicateBody);
     this._args = options.args;
     this._binding = options.binding;
@@ -823,13 +831,24 @@ export class WaitTask {
     }
     if (this._terminated || runCount !== this._runCount) return;
     try {
-      success = await context.evaluateHandle(
-        waitForPredicatePageFunction,
-        this._predicateBody,
-        this._polling,
-        this._timeout,
-        ...this._args
-      );
+      if (this._root) {
+        success = await this._root.evaluateHandle(
+          waitForPredicatePageFunction,
+          this._predicateBody,
+          this._polling,
+          this._timeout,
+          ...this._args
+        );
+      } else {
+        success = await context.evaluateHandle(
+          waitForPredicatePageFunction,
+          null,
+          this._predicateBody,
+          this._polling,
+          this._timeout,
+          ...this._args
+        );
+      }
     } catch (error_) {
       error = error_;
     }
@@ -890,11 +909,13 @@ export class WaitTask {
 }
 
 async function waitForPredicatePageFunction(
+  root: Element | Document | null,
   predicateBody: string,
   polling: string,
   timeout: number,
   ...args: unknown[]
 ): Promise<unknown> {
+  root = root || document;
   const predicate = new Function('...args', predicateBody);
   let timedOut = false;
   if (timeout) setTimeout(() => (timedOut = true), timeout);
@@ -906,7 +927,7 @@ async function waitForPredicatePageFunction(
    * @returns {!Promise<*>}
    */
   async function pollMutation(): Promise<unknown> {
-    const success = await predicate(...args);
+    const success = await predicate(root, ...args);
     if (success) return Promise.resolve(success);
 
     let fulfill;
@@ -916,13 +937,13 @@ async function waitForPredicatePageFunction(
         observer.disconnect();
         fulfill();
       }
-      const success = await predicate(...args);
+      const success = await predicate(root, ...args);
       if (success) {
         observer.disconnect();
         fulfill(success);
       }
     });
-    observer.observe(document, {
+    observer.observe(root, {
       childList: true,
       subtree: true,
       attributes: true,
@@ -941,7 +962,7 @@ async function waitForPredicatePageFunction(
         fulfill();
         return;
       }
-      const success = await predicate(...args);
+      const success = await predicate(root, ...args);
       if (success) fulfill(success);
       else requestAnimationFrame(onRaf);
     }
@@ -958,7 +979,7 @@ async function waitForPredicatePageFunction(
         fulfill();
         return;
       }
-      const success = await predicate(...args);
+      const success = await predicate(root, ...args);
       if (success) fulfill(success);
       else setTimeout(onTimeout, pollInterval);
     }

src/common/JSHandle.ts

@@ -351,6 +351,50 @@ export class ElementHandle<
     this._frameManager = frameManager;
   }
 
+  /**
+   * Wait for the `selector` to appear within the element. If at the moment of calling the
+   * method the `selector` already exists, the method will return immediately. If
+   * the `selector` doesn't appear after the `timeout` milliseconds of waiting, the
+   * function will throw.
+   *
+   * This method does not work across navigations or if the element is detached from DOM.
+   *
+   * @param selector - A
+   * {@link https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Selectors | selector}
+   * of an element to wait for
+   * @param options - Optional waiting parameters
+   * @returns Promise which resolves when element specified by selector string
+   * is added to DOM. Resolves to `null` if waiting for hidden: `true` and
+   * selector is not found in DOM.
+   * @remarks
+   * The optional parameters in `options` are:
+   *
+   * - `visible`: wait for the selected element to be present in DOM and to be
+   * visible, i.e. to not have `display: none` or `visibility: hidden` CSS
+   * properties. Defaults to `false`.
+   *
+   * - `hidden`: wait for the selected element to not be found in the DOM or to be hidden,
+   * i.e. have `display: none` or `visibility: hidden` CSS properties. Defaults to
+   * `false`.
+   *
+   * - `timeout`: maximum time to wait in milliseconds. Defaults to `30000`
+   * (30 seconds). Pass `0` to disable timeout. The default value can be changed
+   * by using the {@link Page.setDefaultTimeout} method.
+   */
+  waitForSelector(
+    selector: string,
+    options: {
+      visible?: boolean;
+      hidden?: boolean;
+      timeout?: number;
+    } = {}
+  ): Promise<ElementHandle | null> {
+    return this._context._world.waitForSelector(selector, {
+      ...options,
+      root: this,
+    });
+  }
+
   asElement(): ElementHandle<ElementType> | null {
     return this;
   }

test/elementhandle.spec.ts

@@ -257,6 +257,29 @@ describe('ElementHandle specs', function () {
     });
   });
 
+  describe('Element.waitForSelector', () => {
+    it('should wait correctly with waitForSelector on an element', async () => {
+      const { page } = getTestState();
+      const waitFor = page.waitForSelector('.foo');
+      // Set the page content after the waitFor has been started.
+      await page.setContent(
+        '<div id="not-foo"></div><div class="bar">bar2</div><div class="foo">Foo1</div>'
+      );
+      let element = await waitFor;
+      expect(element).toBeDefined();
+
+      const innerWaitFor = element.waitForSelector('.bar');
+      await element.evaluate((el) => {
+        el.innerHTML = '<div class="bar">bar1</div>';
+      });
+      element = await innerWaitFor;
+      expect(element).toBeDefined();
+      expect(
+        await element.evaluate((el: HTMLElement) => el.innerText)
+      ).toStrictEqual('bar1');
+    });
+  });
+
   describe('ElementHandle.hover', function () {
     it('should work', async () => {
       const { page, server } = getTestState();
@@ -419,6 +442,33 @@ describe('ElementHandle specs', function () {
       expect(element).toBeDefined();
     });
 
+    it('should wait correctly with waitForSelector on an element', async () => {
+      const { page, puppeteer } = getTestState();
+      puppeteer.registerCustomQueryHandler('getByClass', {
+        queryOne: (element, selector) => element.querySelector(`.${selector}`),
+      });
+      const waitFor = page.waitForSelector('getByClass/foo');
+
+      // Set the page content after the waitFor has been started.
+      await page.setContent(
+        '<div id="not-foo"></div><div class="bar">bar2</div><div class="foo">Foo1</div>'
+      );
+      let element = await waitFor;
+      expect(element).toBeDefined();
+
+      const innerWaitFor = element.waitForSelector('getByClass/bar');
+
+      await element.evaluate((el) => {
+        el.innerHTML = '<div class="bar">bar1</div>';
+      });
+
+      element = await innerWaitFor;
+      expect(element).toBeDefined();
+      expect(
+        await element.evaluate((el: HTMLElement) => el.innerText)
+      ).toStrictEqual('bar1');
+    });
+
     it('should wait correctly with waitFor', async () => {
       /* page.waitFor is deprecated so we silence the warning to avoid test noise */
       sinon.stub(console, 'warn').callsFake(() => {});