Page.waitForFunction() method

Waits for a function to finish evaluating in the page's context.

Signature:

class Page {
  waitForFunction<
    Params extends unknown[],
    Func extends EvaluateFunc<Params> = EvaluateFunc<Params>
  >(
    pageFunction: Func | string,
    options?: {
      timeout?: number;
      polling?: string | number;
    },
    ...args: Params
  ): Promise<HandleFor<Awaited<ReturnType<Func>>>>;
}

Parameters

Parameter	Type	Description
pageFunction	Func | string	Function to be evaluated in browser context
options	{ timeout?: number; polling?: string | number; }	(Optional) Optional waiting parameters - 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() method.
args	Params	Arguments to pass to pageFunction

Returns:

Promise<HandleFor<Awaited<ReturnType<Func>>>>

A Promise which resolves to a JSHandle/ElementHandle of the the pageFunction's return value.

Example 1

The Page.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();
})();

Example 2

To pass arguments from node.js to the predicate of Page.waitForFunction() function:

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

Example 3

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 avatar
    const img = document.createElement('img');
    img.src = githubUser.avatar_url;
    // wait 3 seconds
    await new Promise((resolve, reject) => setTimeout(resolve, 3000));
    img.remove();
  },
  {},
  username
);