TypeScript definitions for process.env.NODE_ENV?

Question

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;