JavaScript Tester: Run and Test Code in Your Browser
Use the JavaScript Tester to write code and tests side by side, then run them in an isolated Web Worker. Its built-in test runner supports describe, it/test, expect matchers, beforeEach/afterEach hooks, and async tests. Configure the timeout for a test run, and use the Stop button to stop an infinite loop.
JavaScript Tester is a browser-based JavaScript testing tool for writing code and tests side by side. It runs your tests in an isolated Web Worker, so you can check JavaScript behavior without first wiring the test into your application. The built-in mini test runner supports describe, it/test, expect, beforeEach/afterEach, and async tests.
Organize test cases with describe and it or test, then use expect with matchers such as toBe, toEqual, toContain, and toThrow. The tool also supports a configurable timeout and a Stop button to kill infinite loops. These features let you run checks against your code and stop execution if a loop does not finish.
JavaScript is a programming language, while a test runner provides a way to describe expected behavior and check code against it. Testing an expression or a small piece of code before integrating it into an application can help you explore its behavior and check edge cases. The supported matchers let you express different kinds of expectations in your tests.
JavaScript Tester runs entirely in your browser: your input is processed on your device and is not uploaded, stored, or sent to a server. It has no server dependency, so after the page has loaded, it can keep working offline. Developers and DevOps engineers can use it to try JavaScript code, build focused tests, and check behavior before shipping changes.
Step 1: Enter the JavaScript code you want to test. You can paste or drop your content into the tool.
Step 2: Add tests using describe and it or test, with expect assertions to check the behavior you want.
Step 3: Choose supported matchers such as toBe, toEqual, toContain, or toThrow, and add beforeEach/afterEach hooks if needed.
Step 4: Set a timeout for the test run if you want to configure how long it can run.
Step 5: Run the tests and review the results. If an infinite loop occurs, use the Stop button to stop execution.
Use case: Try a JavaScript expression against real input and check what it matches before using it in an application.
Use case: Iterate on an expression without saving a file or wiring it into your app first.
Use case: Check edge cases with test assertions before shipping a change.
Use case: Write a small suite with describe and it/test to organize checks for a piece of JavaScript code.
Use case: Use toThrow to test whether code throws an error, or toContain to check for a value in a collection.
Use case: Add beforeEach or afterEach hooks when your tests need setup or cleanup around individual cases.
Use case: Run async tests in the built-in test runner to check asynchronous code behavior.
Use case: Set a timeout for a test run and use Stop if an infinite loop prevents it from finishing.