Open source


Adds a script which will be evaluated in one of the following scenarios:

  • Whenever a page is created in the browserContext or is navigated.
  • Whenever a child [frame](<page>) is attached or navigated in any page in the browserContext. In this case, the script is evaluated in the context of the newly attached [frame](<page>).

The script is evaluated after the document is created but before any of its scripts are run. This is useful to amend the JavaScript environment, for example, to override Math.random.


import { browser } from 'k6/experimental/browser';
import { check } from 'k6';

export const options = {
  scenarios: {
    browser: {
      executor: 'shared-iterations',
      options: {
        browser: {
          type: 'chromium',

export default async function () {
  const browserContext = browser.newContext();

  // This will execute and override the existing implementation of Math.random.
  browserContext.addInitScript('Math.random = function(){return 0}');

  const page = browserContext.newPage();

  // In this example we are going to set the content manually, so we first
  // navigate to about:blank which will execute the init script, before setting
  // the content on the page.
  await page.goto('about:blank');

      <div id="random">waiting...</div>
        document.getElementById('random').textContent = Math.random();

  check(page, {
    zero: (p) => p.locator('#random').textContent() == '0',