RunJS

About

RunJS is a JavaScript playground for the desktop, available for macOS as a Universal .app with a free download. It works as a scratchpad where your code runs as you type, with built-in Node.js and browser environments and support for npm packages. Reviewers describe each line being evaluated separately, with output shown on the right, and note support for TypeScript, Babel transpilation, and importing Node modules from a folder.

You can use RunJS to sketch ideas, test a regex, call an API, or try a package without adding any of it to your project. You can inspect any value without modifying your code, and use Magic Comments and Logpoints to log values without console.log. The app also lets you install npm packages, experiment with new libraries and frameworks, save and reuse code snippets in a snippet library, and generate and run code with AI chat.

The site presents RunJS as useful for learning, completing code challenges, and creative experimentation. Testimonials from developers and teachers describe it as a tool for debugging, testing ideas quickly, and explaining JavaScript behavior to others.