Page | /tests/deps.ts | fresh@1.4.3

method Page.prototype.waitForFunction

Re-export

import { Page } from "https://deno.land/x/fresh@1.4.3/tests/deps.ts";

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>>>>

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

Examples

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();
})();

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

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

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
);

Type Parameters

Params extends unknown[]

optional

Func extends EvaluateFunc<Params> = EvaluateFunc<Params>

Parameters

pageFunction: Func | string

Function to be evaluated in browser context

optional

options: { timeout?: number; polling?: string | number; }

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.