safe Object property access, using ES6's Proxy and also make it typed!

safe-object.ts

/*
Using ES6's Proxy for safe Object property access
This gist is inspired from:
https://gidi.io/2016/02/07/using-es6-s-proxy-for-safe-object-property-access.html
*/

const isObject = (obj: any) => obj && typeof obj === "object";
const hasKey = (obj: any, key: string | number | symbol) => key in obj;

const UndefinedObj: ProxyHandler<{}> = new Proxy(
  {},
  { get: () => UndefinedObj }
);

const either = (val: any, fallback: any) =>
  val === UndefinedObj ? fallback : val;

type NoNullField<T> = { [P in keyof T]-?: NoNullField<NonNullable<T[P]>> };

function safe<T extends object>(obj: T): NoNullField<T> {
  return new Proxy(obj, {
    get(target, name) {
      if (hasKey(target, name)) {
        const value = target[name];
        if (isObject(target[name])) {
          return safe(target[name]) as NoNullField<typeof value>;
        } else {
          return value;
        }
      }
      return UndefinedObj;
    }
  }) as NoNullField<T>;
}

export { safe, either };


// Example: 
const x: { a?: { b: number } } = { a: { b: 3 } };
safe(x).a.b; // no compile error that x.a is possibly undefined