Jest vs Vitest in 2026 -- Which JavaScript Test Runner Should You Use?
A comprehensive comparison of Jest and Vitest in 2026. Covers speed benchmarks, ESM support, TypeScript, mocking, configuration, and migration guide from Jest to Vitest.
Jest has been the default JavaScript test runner for years. But Vitest, built on top of Vite's blazing-fast transformation pipeline, offers a compelling alternative. If you are choosing a test runner in 2026, this guide breaks down exactly when to use each one.
Key Takeaways
- Vitest is 10-20x faster than Jest on large codebases thanks to native ESM and Vite's transform pipeline
- Jest has the larger ecosystem with more plugins, integrations, and community resources
- Vitest is API-compatible with Jest -- most tests migrate with minimal changes
- For Vite-based projects (React, Vue, Svelte), Vitest is the clear choice
- For large enterprise codebases with extensive Jest infrastructure, migration may not be worth the effort
- Both frameworks work well with AI coding agents when paired with the right QA skills
Architecture: Why Vitest Is Faster
Jest was built in the CommonJS era. It transforms every file using Babel or ts-jest before running it. Each test file spawns a worker, and module resolution goes through Jest's custom module system.
Vitest leverages Vite's native ESM transformation pipeline. It uses esbuild for TypeScript transpilation (which is orders of magnitude faster than Babel) and serves modules using Vite's dev server architecture.
The result is dramatically faster startup and execution:
| Metric | Jest | Vitest |
|---|---|---|
| Cold start (500 tests) | ~12s | ~1.5s |
| Watch mode re-run | ~4s | ~0.2s |
| TypeScript transform | Babel/ts-jest (slow) | esbuild (native) |
| Module system | CommonJS (transforms ESM) | Native ESM |
| Config reuse | Separate jest.config | Shares vite.config |
Configuration Comparison
Jest Configuration
// jest.config.ts
export default {
preset: 'ts-jest',
testEnvironment: 'jsdom',
moduleNameMapper: {
'^@/(.*)$': '<rootDir>/src/$1',
'\\.(css|less)$': 'identity-obj-proxy',
},
setupFilesAfterSetup: ['./jest.setup.ts'],
transform: {
'^.+\\.tsx?$': 'ts-jest',
},
collectCoverageFrom: ['src/**/*.{ts,tsx}'],
};
Vitest Configuration
// vitest.config.ts (or just add to vite.config.ts)
import { defineConfig } from 'vitest/config';
export default defineConfig({
test: {
environment: 'jsdom',
setupFiles: './vitest.setup.ts',
coverage: {
include: ['src/**/*.{ts,tsx}'],
},
},
resolve: {
alias: { '@': './src' },
},
});
Vitest's config is simpler because it inherits path aliases, transforms, and plugins from your Vite config. No separate module mappers, no transform configuration, no CSS mocking.
Side-by-Side Test Comparison
The good news: Vitest's API is almost identical to Jest's.
Jest
// sum.test.ts (Jest)
import { sum } from './sum';
describe('sum', () => {
it('adds two numbers', () => {
expect(sum(1, 2)).toBe(3);
});
it('handles negative numbers', () => {
expect(sum(-1, -2)).toBe(-3);
});
it.each([
[1, 2, 3],
[0, 0, 0],
[-1, 1, 0],
])('sum(%i, %i) = %i', (a, b, expected) => {
expect(sum(a, b)).toBe(expected);
});
});
Vitest
// sum.test.ts (Vitest)
import { describe, it, expect } from 'vitest';
import { sum } from './sum';
describe('sum', () => {
it('adds two numbers', () => {
expect(sum(1, 2)).toBe(3);
});
it('handles negative numbers', () => {
expect(sum(-1, -2)).toBe(-3);
});
it.each([
[1, 2, 3],
[0, 0, 0],
[-1, 1, 0],
])('sum(%i, %i) = %i', (a, b, expected) => {
expect(sum(a, b)).toBe(expected);
});
});
The only difference is the import line. Vitest requires explicit imports of describe, it, expect (or you can set globals: true in config to match Jest's behavior exactly).
TypeScript Support
Jest requires either ts-jest (slow, full type-checking) or @swc/jest (fast, no type-checking) for TypeScript support. Configuration is often the most frustrating part of setting up Jest with TypeScript.
Vitest supports TypeScript out of the box via esbuild. No configuration needed. It strips types at near-native speed without a separate transform step.
# Jest TypeScript setup
npm install --save-dev jest ts-jest @types/jest
npx ts-jest config:init
# Vitest TypeScript setup
npm install --save-dev vitest
# Done. It just works.
Mocking Comparison
Jest Mocking
// Jest auto-mocking
jest.mock('./api-client');
import { fetchUser } from './api-client';
const mockFetchUser = fetchUser as jest.MockedFunction<typeof fetchUser>;
mockFetchUser.mockResolvedValue({ id: 1, name: 'Test' });
Vitest Mocking
// Vitest mocking
import { vi } from 'vitest';
vi.mock('./api-client');
import { fetchUser } from './api-client';
const mockFetchUser = vi.mocked(fetchUser);
mockFetchUser.mockResolvedValue({ id: 1, name: 'Test' });
The APIs are nearly identical. jest.fn() becomes vi.fn(), jest.mock() becomes vi.mock(), jest.spyOn() becomes vi.spyOn(). Vitest also adds vi.mocked() as a cleaner TypeScript utility.
Watch Mode
Jest's watch mode re-runs affected tests when files change. It works, but cold starts are slow and the file watcher can be resource-heavy.
Vitest's watch mode is its killer feature. Powered by Vite's HMR (Hot Module Replacement), it re-runs only the affected tests in milliseconds. On a 500-test codebase, a single file change re-runs in under 200ms compared to Jest's 3-5 seconds.
# Jest watch
npx jest --watch
# Vitest watch (default mode)
npx vitest
Coverage
Both frameworks support coverage via istanbul or v8:
| Feature | Jest | Vitest |
|---|---|---|
| Coverage provider | istanbul (default), v8 | v8 (default), istanbul |
| Built-in | Yes (--coverage) | Yes (--coverage) |
| HTML reporter | Yes | Yes |
| Threshold enforcement | Yes | Yes |
| Speed | Moderate | Faster (v8 native) |
# Jest
npx jest --coverage
# Vitest
npx vitest run --coverage
Snapshot Testing
Both frameworks support snapshot testing with identical syntax:
// Works in both Jest and Vitest
expect(component).toMatchSnapshot();
expect(component).toMatchInlineSnapshot();
Vitest even reads existing Jest snapshot files, making migration seamless.
Full Comparison Table
| Feature | Jest | Vitest |
|---|---|---|
| Speed (cold start) | Slow (~12s/500 tests) | Fast (~1.5s/500 tests) |
| Watch mode | Seconds | Milliseconds (HMR) |
| ESM support | Experimental, flag needed | Native, first-class |
| TypeScript | Requires ts-jest or @swc/jest | Built-in via esbuild |
| Configuration | Verbose, separate config | Minimal, shares vite.config |
| Mocking API | jest.fn/mock/spyOn | vi.fn/mock/spyOn (compatible) |
| Snapshot testing | Full support | Full support (reads Jest snapshots) |
| Coverage | istanbul/v8 | istanbul/v8 |
| Browser testing | Experimental | Built-in browser mode |
| UI mode | No | vitest --ui with visual dashboard |
| Concurrent tests | Limited | it.concurrent built-in |
| Ecosystem | Massive (10,000+ packages) | Growing (compatible with many Jest plugins) |
| Community | Very large | Rapidly growing |
| Learning curve | Moderate | Easy (if you know Jest) |
| Framework integration | Manual setup | First-class Vite/React/Vue/Svelte |
| Component testing | React Testing Library | React Testing Library + Browser mode |
Migration from Jest to Vitest
Step 1: Install Vitest
npm install --save-dev vitest
npm uninstall ts-jest @types/jest
Step 2: Update Config
Replace jest.config.ts with vitest.config.ts, or add a test block to your existing vite.config.ts.
Step 3: Find and Replace
| Jest | Vitest |
|---|---|
jest.fn() | vi.fn() |
jest.mock() | vi.mock() |
jest.spyOn() | vi.spyOn() |
jest.useFakeTimers() | vi.useFakeTimers() |
jest.clearAllMocks() | vi.clearAllMocks() |
Or set globals: true in your Vitest config to keep using the same globals-based syntax without changing test files.
Step 4: Update Scripts
{
"scripts": {
"test": "vitest run",
"test:watch": "vitest",
"test:coverage": "vitest run --coverage"
}
}
Most Jest test suites migrate to Vitest in under an hour.
When Jest Still Wins
- Large enterprise codebases with thousands of tests and deep Jest customizations
- Non-Vite projects using Webpack, where Vitest's speed advantage is less relevant
- React Native projects, where Jest has better integration
- Extensive custom reporters and plugins that haven't been ported to Vitest yet
- Teams familiar with Jest where the speed improvement doesn't justify retraining
When to Choose Vitest
- Vite-based projects (React + Vite, Vue, Svelte, SvelteKit, Nuxt)
- New projects where you want the fastest possible test runner
- TypeScript-first codebases that want zero-config TS support
- Developer experience matters and you want sub-second watch mode feedback
- ESM-native packages that don't work well with Jest's CommonJS transform
How QA Skills Help
Whether you use Jest or Vitest, QA skills teach your AI agent the patterns that matter -- test structure, mocking strategies, coverage goals, and testing best practices.
npx @qaskills/cli add jest-unit
npx @qaskills/cli add vitest-testing
The jest-unit skill covers assertion patterns, mock factories, snapshot testing, and coverage configuration. The vitest-testing skill adds Vite-specific patterns, browser mode testing, and concurrent test strategies.
Combine these with TDD practices from our TDD best practices guide for maximum impact. Browse all skills at qaskills.sh/skills or get started in 30 seconds.
Conclusion
In 2026, Vitest is the better choice for most JavaScript projects, especially those built on Vite. Its speed advantage is not marginal -- it is transformative for developer experience. Sub-second feedback loops change how you write code.
Jest remains a solid choice for large existing codebases, React Native projects, and teams with deep Jest infrastructure. There is no rush to migrate if Jest is working well for you.
For new projects, start with Vitest. Install a QA skill to give your AI agent expert testing knowledge from day one:
npx @qaskills/cli add vitest-testing
Written by Pramod Dutta, founder of The Testing Academy and QASkills.sh.