What does JavaScript Test Runner actually do?

The JS test runner executes small assertions in the browser against code you paste. It is not Jest, not your CI, and not a Node environment. Browser globals exist. Node builtins such as fs do not.

When should I use JavaScript Test Runner?

Use it to try a pure function and a couple of asserts.

When should I not use JavaScript Test Runner?

Do not run untrusted code you would not paste into DevTools.

What does JavaScript Test Runner not do?

No module installer. A green run here is not a pipeline result.

JavaScript Test Runner

Write and run JavaScript unit tests in your browser. Includes assert library and async support. Free online — runs locally, no upload.

Test Code

// Available: assert.equal, assert.notEqual, assert.truthy, assert.falsy,
// assert.deepEqual, assert.throws, assert.greaterThan, assert.lessThan, assert.contains

Results (0)

Click "Run Tests" to execute

Write tests as a tests object with named test cases. Each test has a descriptionand a fn that runs assertions (sync or async). Use assert.* methods to verify behavior. Tests run in your browser — no server.

Search tools

JavaScript Test Runner