84 lines
2.9 KiB
Markdown
84 lines
2.9 KiB
Markdown
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<!-- Do not edit this file. It is automatically generated by API Documenter. -->
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[Home](./index.md) > [puppeteer](./puppeteer.md) > [Page](./puppeteer.page.md) > [waitForFunction](./puppeteer.page.waitforfunction.md)
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## Page.waitForFunction() method
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The `waitForFunction` can be used to observe viewport size change:
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```
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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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To pass arguments from node.js to the predicate of `page.waitForFunction` function:
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```
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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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The predicate of `page.waitForFunction` can be asynchronous too:
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```
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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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<b>Signature:</b>
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```typescript
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waitForFunction(pageFunction: Function | string, options?: {
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timeout?: number;
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polling?: string | number;
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}, ...args: SerializableOrJSHandle[]): Promise<JSHandle>;
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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 | Function \| string | Function to be evaluated in browser context |
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| options | { timeout?: number; polling?: string \| number; } | Optional waiting parameters |
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| args | [SerializableOrJSHandle](./puppeteer.serializableorjshandle.md)\[\] | Arguments to pass to <code>pageFunction</code> |
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<b>Returns:</b>
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Promise<[JSHandle](./puppeteer.jshandle.md)>
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Promise which resolves when the `pageFunction` returns a truthy value. It resolves to a JSHandle of the truthy value.
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The optional waiting parameter can be:
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- `Polling`: An interval at which the `pageFunction` is executed, defaults to `raf`. If `polling` 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:<br/> - `raf`: to constantly execute `pageFunction` in `requestAnimationFrame` callback. This is the tightest polling mode which is suitable to observe styling changes.<br/> - `mutation`: to execute pageFunction on every DOM mutation.
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- `timeout`: 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)](./puppeteer.page.setdefaulttimeout.md) method.
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