waitForFunction method

Parameters:

• pageFunction: Function to be evaluated in browser context
• polling: An interval at which the pageFunction is executed, defaults to everyFrame.
  • Polling.everyFrame: to constantly execute pageFunction in requestAnimationFrame callback. This is the tightest polling mode which is suitable to observe styling changes.
  • Polling.mutation: to execute pageFunction on every DOM mutation.
  • Polling.interval: An interval at which the function would be executed
• args: Arguments to pass to pageFunction

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

The waitForFunction can be used to observe viewport size change:

import 'package:puppeteer/puppeteer.dart';

void main() async {
  var browser = await puppeteer.launch();
  var page = await browser.newPage();
  var watchDog = page.mainFrame.waitForFunction('window.innerWidth < 100');
  await page.setViewport(DeviceViewport(width: 50, height: 50));
  await watchDog;
  await browser.close();
}

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

var selector = '.foo';
await page.mainFrame.waitForFunction(
    'selector => !!document.querySelector(selector)',
    args: [selector]);