Skip to main content

Intro to RunJS

RunJS is a desktop app for rapidly prototyping JavaScript and TypeScript. Write code on the left, see results on the right — no project setup, no build step, no config.

RunJS demo

Use cases​

  • Experimenting with an API or library — pull in an npm package and explore its surface without spinning up a project.
  • Learning a language feature — try new ECMAScript or TypeScript syntax and see what it evaluates to.
  • Prototyping logic — work out a tricky function in isolation before pasting it into a real codebase.
  • Quick data transforms — paste in JSON, CSV, or a log dump and reshape it with a few lines of code.
  • Hitting API endpoints — fire fetch requests at a REST or GraphQL API and inspect the response inline.
  • Prototyping UI — sketch a React component, an SVG, or a canvas animation and see it render in the web view.
  • Browser API experiments — play with Canvas, WebGL, or the Web Audio API without setting up an HTML page.
  • Debugging — drop logpoints or magic comments into a snippet to inspect intermediate values without console.log.
  • One-off scripts — run a calculation, query a local file, or kick off a small Node task without committing anything to disk.