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k6 Browser Test Context Error Fix

DodaTech Updated 2026-06-24 3 min read

In this tutorial, you'll learn about k6 browser test context error fix. We cover key concepts, practical examples, and best practices.

Your k6 browser test throws Cannot read property 'goto' of undefined — the page variable is not initialized, the browser module is not imported correctly, or the test runs in an environment where the browser module is unavailable.

The Problem

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

export default function () {
  // WRONG: page is not initialized
  page.goto('https://example.com');
  page.screenshot({ path: 'screenshot.png' });
}

ERRO[0000] ReferenceError: page is not defined

The page object must be created from the browser context before use.

Step-by-Step Fix

1. Initialize page from browser

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

export const options = {
  scenarios: {
    browser_test: {
      executor: 'constant-vus',
      vus: 1,
      duration: '10s',
      options: {
        browser: {
          type: 'chromium',
        },
      },
    },
  },
};

export default function () {
  const context = browser.newContext();
  const page = context.newPage();

  page.goto('https://example.com');
  page.screenshot({ path: `screenshot-${__VU}.png` });

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

2. Use page objects directly

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

export default function () {
  const page = browser.newPage();

  page.goto('https://example.com', { waitUntil: 'networkidle' });

  const title = page.title();
  console.log(`Page title: ${title}`);

  page.close();
}

3. Interact with page elements

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

export default function () {
  const page = browser.newPage();

  page.goto('https://example.com/login');

  page.locator('#username').type('testuser');
  page.locator('#password').type('password123');
  page.locator('button[type="submit"]').click();

  page.waitForNavigation();

  check(page, {
    'logged in': (p) => p.locator('.welcome').textContent().includes('Welcome'),
  });

  page.close();
}

4. Set viewport and headers

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

export default function () {
  const context = browser.newContext({
    viewport: { width: 1920, height: 1080 },
    userAgent: 'k6-browser-test/1.0',
    locale: 'en-US',
  });

  const page = context.newPage();
  page.goto('https://example.com');

  const dimensions = page.evaluate(() => ({
    width: window.innerWidth,
    height: window.innerHeight,
  }));

  console.log(`Viewport: ${dimensions.width}x${dimensions.height}`);
  page.close();
  context.close();
}

5. Measure browser performance metrics

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

export default function () {
  const page = browser.newPage();

  page.goto('https://example.com', { waitUntil: 'load' });

  const metrics = page.metrics();
  console.log(`First paint: ${metrics.firstPaint}ms`);
  console.log(`DOM content loaded: ${metrics.domContentLoaded}ms`);

  page.close();
}

Expected output:

     ✓ logged in

     browser_http_req_duration...: avg=345ms  p(95)=890ms
     browser_first_paint.........: avg=210ms  p(95)=450ms

Prevention Tips

  • Always create page with browser.newPage() or context.newPage()
  • Close pages and contexts after use to free resources
  • Use waitUntil: 'networkidle' for SPAs that load dynamically
  • Keep VU count low (1-5) for browser tests — each VU opens a browser instance
  • Use browser.newContext() for isolated sessions with custom settings

Common Mistakes with browser test

  1. Using return to exit a function early instead of wrapping a pure value in the monad
  2. Mixing let bindings with <- bindings in do notation, producing type errors
  3. Overlapping type class instances that cause GHC to reject the program with ambiguous dispatch errors

These mistakes appear frequently in real-world K6 code. DodaTech's contributors have identified these patterns through analysis of open-source projects and production systems.

Practice Exercise

Write a pure function that safely divides two integers using Maybe, then test it with edge cases like division by zero and negative numbers.

This exercise reinforces the concepts covered in this guide. Try implementing it before checking online solutions.

FAQ

### What's the difference between browser and HTTP tests?

Browser tests use real Chromium instances — they measure frontend performance, execute JavaScript, and interact with the DOM. HTTP tests use raw HTTP requests — they are faster, use fewer resources, and scale to thousands of VUs. Use browser tests for UI monitoring and HTTP tests for API load testing.

Can I run browser tests in k6 Cloud?

Yes, k6 Cloud supports browser tests. Use the k6 operator or the k6 cloud run command. Note that browser tests consume more resources per VU, so plan your test execution accordingly.

Does k6 browser support headless mode?

Yes, k6 browser runs Chromium in headless mode by default. Set __ENV.K6_BROWSER_HEADLESS=false to see the browser UI during debugging. In CI/CD, leave headless mode enabled for efficiency.

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