Unit and functional testing are essential for ensuring the quality of JavaScript code, and a variety of tools are available to test code within browsers, each offering unique features and advantages. JavaScript remains a dominant language in web development, necessitating continuous testing in agile development processes, with methods like Behavior-Driven Development (BDD) and Test-Driven Development (TDD) emphasizing testing as a core activity. Browsers support JavaScript natively, and tools such as LambdaTest, CodePen, CodeSandbox, JSFiddle, and others facilitate testing directly within the browser without additional installations, allowing developers to verify code functionality across different environments. These tools offer features like real-time collaboration, integration with platforms like GitHub, and support for various JavaScript frameworks, enhancing the testing process. Cloud-based platforms like LambdaTest provide extensive capabilities to test JavaScript across different browsers, devices, and operating systems, streamlining the testing process and ensuring compatibility and performance.