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It’s been a while since tsx became my go-to tool to run TypeScript files. It needs no config and works out of the box most of the time (if not always). But yesterday, I ran into errors running a NestJS project—and it took me a while to realize tsx was the culprit.

NestJS relies heavily on decorators, which are still Stage 3 experimental. You need to explicitly enable them in your tsconfig.json like so:

{
  "compilerOptions": {
    "target": "ES5",
    "experimentalDecorators": true
  }
}

Once enabled, the appropriate metadata gets attached to functions, classes, etc. But here’s the catch: tsx relies on esbuild, which doesn’t support decorators out of the box. You’d need extra plugins to make it work. As of now, there’s an open issue for this, but no plans to address it.

In my case, I was using tsx with nest-commander to run CLI commands. Switching to:

ts-node -r tsconfig-paths/register src/cli/main.ts

made everything work again.

tl;dr

TSX doesn't support TypeScript decorators due to its reliance on esbuild. To work around this, especially in NestJS projects, use ts-node instead.

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tsx doesn’t support decorators

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tsx doesn’t support decorators

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tl;dr