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Signed-off-by: dependabot[bot] <support@github.com> Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com> Co-authored-by: Nikolay Vitkov <nvitkov@chromium.org>
133 lines
2.3 KiB
Markdown
133 lines
2.3 KiB
Markdown
---
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sidebar_label: Page.waitForFunction
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---
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# Page.waitForFunction() method
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Waits for the provided function, `pageFunction`, to return a truthy value when evaluated in the page's context.
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#### Signature:
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```typescript
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class Page {
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waitForFunction<
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Params extends unknown[],
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Func extends EvaluateFunc<Params> = EvaluateFunc<Params>,
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>(
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pageFunction: Func | string,
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options?: FrameWaitForFunctionOptions,
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...args: Params
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): Promise<HandleFor<Awaited<ReturnType<Func>>>>;
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}
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```
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## Parameters
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<table><thead><tr><th>
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Parameter
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</th><th>
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Type
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</th><th>
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Description
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</th></tr></thead>
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<tbody><tr><td>
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pageFunction
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</td><td>
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Func \| string
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</td><td>
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Function to be evaluated in browser context until it returns a truthy value.
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</td></tr>
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<tr><td>
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options
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</td><td>
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[FrameWaitForFunctionOptions](./puppeteer.framewaitforfunctionoptions.md)
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</td><td>
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_(Optional)_ Options for configuring waiting behavior.
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</td></tr>
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<tr><td>
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args
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</td><td>
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Params
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</td><td>
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</td></tr>
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</tbody></table>
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**Returns:**
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Promise<[HandleFor](./puppeteer.handlefor.md)<Awaited<ReturnType<Func>>>>
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## Example 1
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[Page.waitForFunction()](./puppeteer.page.waitforfunction.md) can be used to observe a viewport size change:
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```ts
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import puppeteer from 'puppeteer';
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(async () => {
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const browser = await puppeteer.launch();
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const page = await browser.newPage();
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const watchDog = page.waitForFunction('window.innerWidth < 100');
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await page.setViewport({width: 50, height: 50});
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await watchDog;
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await browser.close();
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})();
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```
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## Example 2
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Arguments can be passed from Node.js to `pageFunction`:
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```ts
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const selector = '.foo';
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await page.waitForFunction(
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selector => !!document.querySelector(selector),
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{},
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selector
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);
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```
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## Example 3
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The provided `pageFunction` can be asynchronous:
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```ts
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const username = 'github-username';
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await page.waitForFunction(
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async username => {
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const githubResponse = await fetch(
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`https://api.github.com/users/${username}`
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);
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const githubUser = await githubResponse.json();
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// show the avatar
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const img = document.createElement('img');
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img.src = githubUser.avatar_url;
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// wait 3 seconds
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await new Promise((resolve, reject) => setTimeout(resolve, 3000));
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img.remove();
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},
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{},
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username
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);
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```
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