Type-safe key mirror

keyMirror.ts

function keyMirror<Obj>(...args: (keyof Obj)[]): Readonly<{ [Key in keyof Obj]: Key }> {
  let obj = {};
  for (let arg of args) {
    Object.defineProperty(obj, arg, {
      configurable: false,
      enumerable: true,
      value: arg,
      writable: false,
    });
  }
  return obj as Readonly<{ [Key in keyof Obj]: Key }>;
}

Example:

const stopLight = keyMirror('red', 'yellow', 'green');

stopLight.red === 'red' // true