#Environment variables

This page describes how Rslib handles import.meta.env.* and process.env.* references in source code when generating library output.

#Default behavior

Rslib handles built-in env preset references differently for each output format:

The preset values in the table follow Rsbuild's environment variable handling; see Rsbuild - Environment Variables for details.

Preserved references can be replaced by a downstream build tool or resolved by the target runtime.

#Replacing with specific values at build time

To replace an environment variable with a specific value when building the library, define it explicitly with source.define:

import { defineConfig } from '@rslib/core';

export default defineConfig({
  source: {
    define: {
      'import.meta.env.MODE': JSON.stringify('production'),
      'process.env.BASE_URL': JSON.stringify('/'),
    },
  },
});