--- title: "addInitScript() | Grafana k6 documentation" description: "Adds an init script." --- > For a curated documentation index, see [llms.txt](/llms.txt). For the complete documentation index, see [llms-full.txt](/llms-full.txt). # addInitScript() Adds a script which will be evaluated in one of the following scenarios: - Whenever a [page](/docs/k6/latest/javascript-api/k6-browser/page/) is created in the [browser context](/docs/k6/latest/javascript-api/k6-browser/browsercontext/) or is navigated. - Whenever a child [frame](/docs/k6/latest/javascript-api/k6-browser/frame/) is attached or navigated in any [page](/docs/k6/latest/javascript-api/k6-browser/page/) in the [browser context](/docs/k6/latest/javascript-api/k6-browser/browsercontext/). In this case, the script is evaluated in the context of the newly attached [frame](/docs/k6/latest/javascript-api/k6-browser/frame/). 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`. ### Returns Expand table | Type | Description | |-----------------|---------------------------------------------------------------------------------------------------------------------------------------------| | `Promise` | A Promise that fulfills when the script has been added to the [browser context](/docs/k6/latest/javascript-api/k6-browser/browsercontext/). | ### Example JavaScript ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy ```javascript import { browser } from 'k6/browser'; import { check } from 'https://jslib.k6.io/k6-utils/1.5.0/index.js'; export const options = { scenarios: { browser: { executor: 'shared-iterations', options: { browser: { type: 'chromium', }, }, }, }, }; export default async function () { const browserContext = await browser.newContext(); // This will execute and override the existing implementation of Math.random. await browserContext.addInitScript('Math.random = function(){return 0}'); const page = await 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'); await page.setContent(`

waiting...

`); await check(page.locator('#random'), { 'is zero': async random => await random.textContent() == '0' }); await page.close(); } ```