ReferenceError: process is not defined in Vite (dev vs build)

The same line of code can crash in Vite’s dev server and then “work” in the production build with an empty value. In my test on Vite 8.3.5, process.env.API_KEY threw process is not defined under vite, and came back undefined with no error after vite build, while process.env.NODE_ENV worked in both. The reason is that process belongs to Node: browsers don’t have it, older bundlers like webpack 4 quietly added a fake one, and Vite doesn’t.

What surprised me is that Vite’s dev server and its production build don’t fail the same way. I ran one small file through both on Vite 8.3.5 and read the results in Chromium, including a dependency that reads process:

So process.env.SOMETHING can crash in development and then “work” in production with an empty value, or the other way round if you only test the build. Either way, the setting never reaches your code.

process.env.NODE_ENV is the exception: Vite replaces it with the mode, in your code and in dependencies, so that one never throws. If the error points at a line with NODE_ENV, look again: the crash is another process reference nearby.

Your own code: use import.meta.env

VITE_API_KEY=your-value

const key = import.meta.env.VITE_API_KEY;

A package that uses process: define it

When the process reference is in a dependency you can’t edit, tell Vite what to replace it with at build time:

// vite.config.js
export default {
  define: {
    'process.env.API_KEY': JSON.stringify('value'),
    'process.platform': JSON.stringify('browser'),
  },
};

The common shortcut: 'process.env': {}

Many answers suggest replacing the whole object:

// vite.config.js
export default { define: { 'process.env': {} } };

This stops the crash for anything under process.env: every one of those expressions became undefined in the dev server and in the build, and NODE_ENV still worked. But it doesn’t create process. process.platform still threw process is not defined in the build, even though it no longer threw in the dev server. If a package reads more than process.env, use a polyfill instead.

A package that needs more of Node: vite-plugin-node-polyfills

npm install -D vite-plugin-node-polyfills

// vite.config.js
import { nodePolyfills } from 'vite-plugin-node-polyfills';
export default { plugins: [nodePolyfills()] };

None of the setups put the non-VITE_ API_KEY from .env into the built files: I searched dist for its value and found nothing.

How this was tested

Windows 11 Pro, Node 24.14.0, Vite 8.3.4, October 18, 2026. A one-file app read process.env.API_KEY, process.platform and import.meta.env values from a .env file, and wrote what it got onto the page. Each version ran in vite (dev server) and vite build with vite preview, opened in Chromium (Claude’s built-in browser), before and after adding define. Every message above is the real output.

November 1, 2026: re-run on Vite 8.3.5 and Node 24.22.1 on GitHub Actions ubuntu-latest, read in Chromium through Playwright, adding process.env.NODE_ENV, a dependency that reads process, define: { 'process.env': {} } and vite-plugin-node-polyfills 0.28.0. The script and the full output are public.