docs/api/puppeteer.page.waitforfunction.md
Waits for the provided function, pageFunction, to return a truthy value when evaluated in the page's context.
class Page {
waitForFunction<
Params extends unknown[],
Func extends EvaluateFunc<Params> = EvaluateFunc<Params>,
>(
pageFunction: Func | string,
options?: FrameWaitForFunctionOptions,
...args: Params
): Promise<HandleFor<Awaited<ReturnType<Func>>>>;
}
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> </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>>>>
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();
Arguments can be passed from Node.js to pageFunction:
const selector = '.foo';
await page.waitForFunction(
selector => !!document.querySelector(selector),
{},
selector,
);
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,
);