Page.waitForFunction() method

Waits for the provided function, pageFunction, to return a truthy value when evaluated in the page's context.

Signature

typescript

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

Parameters

Parameter

</th><th>

Type

</th><th>

Description

</th></tr></thead> <tbody><tr><td>

pageFunction

</td><td>

Func | string

</td><td>

Function to be evaluated in browser context until it returns a truthy value.

</td></tr> <tr><td>

options

</td><td>

FrameWaitForFunctionOptions

</td><td>

(Optional) Options for configuring waiting behavior.

</td></tr> <tr><td>

args

</td><td>

Params

</td><td> </td></tr> </tbody></table>

Returns:

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

Example 1

Page.waitForFunction() can be used to observe a viewport size change:

import puppeteer from 'puppeteer';

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

Arguments can be passed from Node.js to pageFunction:

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

Example 3

The provided pageFunction can be asynchronous:

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,
);