Using Browser Mode

This skill teaches Vitest browser mode setup, configuration, and testing patterns.

Browser Mode Overview

Browser mode runs tests in actual browsers instead of Node.js environments, enabling:

• Real browser APIs (DOM, fetch, localStorage, etc.)
• Visual regression testing
• Component testing with real rendering
• User interaction testing

Provider Packages

Vitest 4.x requires separate provider packages:

Playwright Provider (Recommended)

npm install -D vitest @vitest/browser-playwright

Use when: Need Chromium, Firefox, and WebKit support with modern APIs

WebDriverIO Provider

npm install -D vitest @vitest/browser-webdriverio

Use when: Need broader browser compatibility or existing WebDriverIO infrastructure

Preview Provider

npm install -D vitest @vitest/browser-preview

Use when: Local development preview (not recommended for CI)

For detailed provider setup with all options, see references/provider-setup.md

Quick Setup

Basic Playwright Configuration

import { defineConfig } from 'vitest/config';
import { playwright } from '@vitest/browser-playwright';

export default defineConfig({
  test: {
    browser: {
      enabled: true,
      provider: playwright(),
      instances: [{ browser: 'chromium' }],
      headless: true,
    },
  },
});

Multiple Browsers

instances: [
  { browser: 'chromium' },
  { browser: 'firefox' },
  { browser: 'webkit' },
]

Browser Test APIs

Importing APIs

Correct (Vitest 4.x):

import { page, userEvent } from 'vitest/browser';

Incorrect (Vitest 3.x):

import { page, userEvent } from '@vitest/browser/context';

Page Locators

import { page } from 'vitest/browser';

const button = page.getByRole('button', { name: /submit/i });
const input = page.getByLabelText(/username/i);
const heading = page.getByRole('heading');
const text = page.getByText('Welcome');

User Interactions

import { userEvent } from 'vitest/browser';

await userEvent.fill(input, 'Bob');
await userEvent.click(checkbox);
await userEvent.selectOptions(select, 'value');
await userEvent.hover(element);

Element Assertions

import { expect } from 'vitest';

await expect.element(element).toBeInTheDocument();
await expect.element(element).toBeVisible();
await expect.element(element).toBeEnabled();
await expect.element(element).toHaveTextContent('text');

For complete browser API reference, see references/browser-apis.md

Component Testing

React Components

import { render } from 'vitest-browser-react';

test('submits form', async () => {
  const screen = render(<LoginForm />);

  await screen.getByLabelText(/email/i).fill('user@example.com');
  await screen.getByRole('button').click();
});

For testing React components in browser mode with Vitest, use the testing-components skill for patterns integrating with @testing-library/react and React 19 APIs.

Vue Components

import { render } from 'vitest-browser-vue';

test('component renders', async () => {
  const screen = render(Component, { props: { name: 'Alice' } });

  await expect.element(screen.getByText('Hi, my name is Alice')).toBeInTheDocument();
});

Common Testing Patterns

Form Testing

test('form submission', async () => {
  await userEvent.fill(page.getByLabelText(/email/i), 'user@example.com');
  await userEvent.fill(page.getByLabelText(/password/i), 'password123');
  await userEvent.click(page.getByRole('button', { name: /submit/i }));

  await expect.element(page.getByText('Success')).toBeInTheDocument();
});

For browser-mode testing of Server Action forms, use the securing-server-actions skill for patterns on validation, authentication, and error handling in server actions.

Navigation Testing

test('navigation', async () => {
  await userEvent.click(page.getByRole('link', { name: /about/i }));

  await expect.element(page.getByRole('heading', { name: /about us/i })).toBeInTheDocument();
});

Modal Testing

test('modal dialog', async () => {
  await userEvent.click(page.getByRole('button', { name: /open/i }));

  const dialog = page.getByRole('dialog');
  await expect.element(dialog).toBeVisible();
});

For complete testing patterns including forms, navigation, modals, and more, see references/testing-patterns.md

Visual Regression Testing

test('visual regression', async () => {
  await page.goto('http://localhost:3000');

  const main = page.getByRole('main');
  await expect(main).toMatchScreenshot();
});

Running Browser Tests

CLI Commands

vitest --browser.enabled
vitest --browser.name chromium
vitest --browser.headless=false

Run Specific Project

vitest --project browser

Debugging

Visual Debugging

vitest --browser.headless=false

Enable Traces

vitest --browser.trace on

View traces in Playwright Trace Viewer.

Configuration Options

Headless Mode

browser: {
  headless: process.env.CI ? true : false,
}

Traces

browser: {
  trace: 'retain-on-failure',
}

Viewport

instances: [
  {
    browser: 'chromium',
    context: {
      viewport: { width: 1280, height: 720 },
    },
  },
]

Common Mistakes

1. Using wrong import path: Use vitest/browser, not @vitest/browser/context
2. Missing provider package: Install @vitest/browser-playwright or @vitest/browser-webdriverio
3. Wrong browser instance config: Use instances: [{ browser: 'chromium' }], not name: 'chromium'
4. Not awaiting interactions: Always await user events
5. Not using expect.element: Use expect.element() for element assertions

Migration from Vitest 3.x

Old config:

browser: {
  enabled: true,
  name: 'chromium',
  provider: 'playwright',
}

New config:

import { playwright } from '@vitest/browser-playwright';

browser: {
  enabled: true,
  provider: playwright(),
  instances: [{ browser: 'chromium' }],
}

Old imports:

import { page } from '@vitest/browser/context';

New imports:

import { page } from 'vitest/browser';

References

For detailed browser mode documentation:

• Provider Setup - Playwright, WebDriverIO, Preview setup
• Browser APIs - Complete API reference with examples
• Testing Patterns - Common patterns for forms, modals, navigation

For configuration patterns, see @vitest-4/skills/configuring-vitest-4

For migration guide, see @vitest-4/skills/migrating-to-vitest-4

For complete API reference, see @vitest-4/knowledge/vitest-4-comprehensive.md