Which JavaScript testing framework?

They split into two groups that solve different problems, and most projects use one from each.

Unit and integration runners

• Vitest — the current default for new projects. Vite-native, so it shares your build config, starts quickly, and has a Jest-compatible API.
• Jest — the long-standing standard. Huge ecosystem, batteries included, still the safe choice in an established React or Node codebase.
• node:test — built into Node, zero dependencies. Good for libraries and backend code with no build step.
• Mocha — flexible and unopinionated; you assemble your own assertions (Chai) and mocks (Sinon). Rarely the choice for new work.

End-to-end

• Playwright — drives Chromium, Firefox and WebKit, with auto-waiting that removes most flakiness, plus tracing and parallel execution. The usual recommendation now.
• Cypress — excellent interactive debugging, but runs inside the browser, which limits multi-tab and cross-origin cases.

Companion libraries you will also need

A runner does not know about UI. Testing Library queries the DOM the way a user would — by role and label rather than CSS class — which keeps tests meaningful across refactors. MSW intercepts network requests so tests exercise real code paths without real servers.

How to actually choose

• New Vite project → Vitest + Testing Library + Playwright.
• Existing Jest suite → keep it; migrating is rarely worth the disruption.
• A Node library → node:test avoids dependencies entirely.

The framework matters far less than what you test. A suite of good tests in Mocha beats a poor suite in Vitest, and the common failure is not a bad runner but tests coupled to implementation details, which break on every refactor and eventually get deleted.