puppeteer.page.waitforfunction

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Page.waitForFunction() method

The waitForFunction can be used to observe viewport size change:

const puppeteer = require('puppeteer');(async () => {const browser = await puppeteer.launch();const page = await browser.newPage();const watchDog = page.waitForFunction('window.innerWidth < 100');await page.setViewport({ width: 50, height: 50 });await watchDog;await browser.close();})();

To pass arguments from node.js to the predicate of page.waitForFunction function:

const selector = '.foo';await page.waitForFunction((selector) => !!document.querySelector(selector),{},selector);

The predicate of page.waitForFunction can be asynchronous too:

const username = 'github-username';await page.waitForFunction(async (username) => {const githubResponse = await fetch( `https://api.github.com/users/${username}`);const githubUser = await githubResponse.json();// show the avatarconst img = document.createElement('img');img.src = githubUser.avatar_url;// wait 3 secondsawait new Promise((resolve, reject) => setTimeout(resolve, 3000));img.remove();},{},username);

Signature:

waitForFunction(pageFunction: Function | string, options?: {        timeout?: number;        polling?: string | number;    }, ...args: SerializableOrJSHandle[]): Promise<JSHandle>;

Parameters

Parameter	Type	Description
pageFunction	Function | string	Function to be evaluated in browser context
options	{ timeout?: number; polling?: string | number; }	Optional waiting parameters
args	SerializableOrJSHandle[]	Arguments to pass to pageFunction

Returns:

Promise<JSHandle>

Promise which resolves when the pageFunction returns a truthy value. It resolves to a JSHandle of the truthy value.

The optional waiting parameter can be:

• 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:
  - raf: to constantly execute pageFunction in requestAnimationFrame callback. This is the tightest polling mode which is suitable to observe styling changes.
  - mutation: to execute pageFunction on every DOM mutation.

• 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) method.