93 lines
6.7 KiB
Markdown
93 lines
6.7 KiB
Markdown
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---
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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 a function to finish evaluating 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?: {
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timeout?: number;
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polling?: string | number;
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},
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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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| Parameter | Type | Description |
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| ------------ | ------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
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| pageFunction | Func \| string | Function to be evaluated in browser context |
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| options | { timeout?: number; polling?: string \| number; } | <i>(Optional)</i> Optional waiting parameters - <code>polling</code> - An interval at which the <code>pageFunction</code> is executed, defaults to <code>raf</code>. If <code>polling</code> is a number, then it is treated as an interval in milliseconds at which the function would be executed. If polling is a string, then it can be one of the following values: - <code>raf</code> - to constantly execute <code>pageFunction</code> in <code>requestAnimationFrame</code> callback. This is the tightest polling mode which is suitable to observe styling changes. - <code>mutation</code>- to execute pageFunction on every DOM mutation. - <code>timeout</code> - maximum time to wait for in milliseconds. Defaults to <code>30000</code> (30 seconds). Pass <code>0</code> to disable timeout. The default value can be changed by using the [Page.setDefaultTimeout()](./puppeteer.page.setdefaulttimeout.md) method. |
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| args | Params | Arguments to pass to <code>pageFunction</code> |
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**Returns:**
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Promise<[HandleFor](./puppeteer.handlefor.md)<Awaited<ReturnType<Func>>>>
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A `Promise` which resolves to a JSHandle/ElementHandle of the the `pageFunction`'s return value.
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## Example 1
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The [Page.waitForFunction()](./puppeteer.page.waitforfunction.md) can be used to observe viewport size change:
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```ts
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const puppeteer = require('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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To pass arguments from node.js to the predicate of [Page.waitForFunction()](./puppeteer.page.waitforfunction.md) function:
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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 predicate of [Page.waitForFunction()](./puppeteer.page.waitforfunction.md) can be asynchronous too:
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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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