safe-env.ts

type Safe<T> = { [P in keyof T]: string };

function getSafeEnvironment<T extends {}>(e: T): Safe<T> {
  return new Proxy(e, {
    get: function(env: any, key: string): string {
      const value: any = env[key];
      if (value == null) {
        throw new Error("'" + key + "' environment variable is not set.");
      }
      return value;
    }
  });
}

process.env.FOO
const safeEnv = getSafeEnvironment(process.env);
safeEnv.FOO