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Page.waitForFunction() method

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

Signature:

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

Type

Description

pageFunction

Func | string

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

options

FrameWaitForFunctionOptions

(Optional) Options for configuring waiting behavior.

args

Params

Returns:

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

Example 1

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

import puppeteer from '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

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
);