Sometimes you want to make sure that the JavaScript runtime you're expecting to be running on is the one you're actually running on. With this library, you can detect whether you're actually running inside Node.js, and not Deno or Bun. A single (default) export is provided, and it's a boolean that's true if we're definitely running inside Node.js.

This is done by first checking various globals, and then attempting to alter v8 options, and testing those options have been altered. This is only currently possible in Node.js. The aim is to never have false negatives, and also load quickly if the globals-checking gives us a negative.

• Why not TypeScript or at least JSDoc?
  • The module is very small, and the code does some things that would probably piss off tsc.
  • I don't use TypeScript in my day job, so I tend not to default to it. Don't worry, I'm not one of those haters you see on Twitter.
  • Submit a PR that works correctly and I'll add it.
• Do you just hate Bun and Deno? Are you some Node.js purist? They're both Node.js compatible anyway!
  • No. A lot of code I work with targets very specific runtime things that only work in Node.js, so I want an easy way to bail early if that stuff isn't going to work, even if the runtime is trying to fake that it's Node.js. That's all. Please feel free to create is-really-bun or is-really-deno if that suits your work.
• Isn't checking the globals alone enough?
  • Nope. If folks are trying to fake that they're in Node.js, they can always mess with the globals. Instead we need to do something that's truly impossible in the other platforms, like messing with v8 options.
• Can't a runtime (or runtime user) pretending to be Node.js just intercept loading and replace this module with true?
  • Yes, but if this module is specifically targetted, the runtime (or runtime user) is putting enough effort into faking Node.js that they can handle whatever comes out of that assumption on their own.
• Why no CommonJS?
  • Deno generally doesn't support CommonJS. Yes, it supports it via npm: imports, but that's difficult to use for testing. I'm lazy. Sorry.
  • That's a bad excuse though. Really I should make this work with require. Submit a PR that handles this and I'll add it.

The MIT License. See LICENSE.txt