TypeScript definitions for process.env.NODE_ENV?

Update for Node 8:

Now env is declared as ProcessEnv in DefinitelyTyped.

env: ProcessEnv;

export interface ProcessEnv {
    [key: string]: string | undefined;
}

TypeScript 2 supports npm package type definitions for node. It currently uses the DefinitivelyTyped node.d.ts.

npm install --save-dev @types/node

Pre Node 8 version:

process env is declared as any in DefinitelyTyped node.d.ts.

env: any;

just add before use process.env.NODE_ENV

declare var process : {
  env: {
    NODE_ENV: string
  }
}

To add the node definitions in TypeScript 3+

Use the types from Definitely Typed via npm/yarn:

# Install the latest
npm install --save-dev @types/node
# or
yarn add @types/node --dev

# To install the right types for your version of node (e.g. 12 here)
npm install --save-dev @types/node@^12
yarn add @types/node@^12 --dev

With your types available, the object process.env should be available in your code.

Extending process.env

You can use declaration merging to add new values to process.env. Create a new d.ts file in your project, then add:

declare global {
  namespace NodeJS {
    interface ProcessEnv {
      NODE_ENV?: string
    }
  }
}

This will let you write process.env.NODE_ENV. I'd recommend keeping the ? in unless you have validation that it's set somewhere in the library.

declare namespace NodeJS {
  interface ProcessEnv {
    [key: string]: string | undefined
    NODE_ENV?: 'development' | 'production' | 'test'
  }
}

put the code above in your file global.d.ts

If your are using create-react-app your-app-test --template typescript then already exist a file to set your environment variables.

file name: react-app-env.d.ts located at src folder.

then you can set in that file your custom env variables with this template:

/// <reference types="react-scripts" />
declare global {
    namespace NodeJS {
      interface ProcessEnv {
        GITHUB_AUTH_TOKEN: string;
        NODE_ENV: 'development' | 'production';
        PORT?: string;
        PWD: string;
      }
    }
  }
  
  // If this file has no import/export statements (i.e. is a script)
  // convert it into a module by adding an empty export statement.
  export {}

If you get this error in VSCode, maybe you just need to restart it.