viewportSize()

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

export default async function () {
  const browser = chromium.launch();
  const page = browser.newPage();
  
  page.setViewportSize({
    width: 640,
    height: 480,
  });
  await page.goto('https://test.k6.io/browser.php');

  console.log(page.viewportSize());
}