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Errors / JavaScript errors

Uncaught ReferenceError: process is not defined

Code written for a server ran in the visitor's browser, where that part does not exist.

The script, often the whole app bundle, stops on load: a blank page.

Why it happens

  • A dependency reads process.env and the bundler no longer fills it in: webpack 5 and Vite stopped adding Node's globals for the browser.
  • App code reading process.env.SOMETHING in Vite, where it is import.meta.env instead.

How to fix it

  1. In Vite, use import.meta.env.VITE_…, or define: { "process.env": {} } for a library that only reads it.
  2. In webpack 5, DefinePlugin for the values that are read, or ProvidePlugin with the process/browser package.
  3. Check the library for a browser build before shimming it.

Whose problem it is

Usually the site's own code or settings.

Does your site have it?

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Often seen with

  • require is not definedA file written for a server's module system was sent to the browser as it is.
  • x is not definedA script used a name nobody declared, usually because another script it depends on did not load first.