Add core to inject k6 object into window

[ankur22]

What?

The change injects window.k6 = {}; into all browser contexts and subsequent pages that are created.

Why?

In some cases we want to pass information to other apps to allow them to infer who is performing requests against a website. For now we're exposing an empty object, but we hope to extend the object with meta data that will be useful for other apps that have been instrumented on the website.

Test

To test this change you can run the following k6 script, which will give you enough time to go into the chrome dev tools console and type in window.k6 which should return an empty object ({}).

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

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

export default async function () {
  const page = browser.newPage();
  await page.goto("https://test.k6.io");

  sleep(20);

  page.close();
  context.close();
}

Checklist

• I have performed a self-review of my code
• I have added tests for my changes
• I have commented on my code, particularly in hard-to-understand areas

Closes: #1017

[inancgumus]

Looks good to me overall, and I'm excited about this feature! 😊

I do have a few points for us to chat about. Also, it might be helpful to include some comments in the code to clarify the role of k6ObjScript.

[inancgumus]

Nice job, thanks!

[ka3de]

LGTM 👏