Why doesn't TypeScript compiler detect missing properties on object created with Object.create(null)?

Question

I have this code:

'use strict';

type Bar = 'a' | 'b';
type FooIntermidiate = {
  [p in Bar]: string;
};
type Foo = Required<FooIntermidiate>;

console.log(getFoo());

function getFoo(): Foo {
  const rv = Object.create(null);
  //const rv = {  };
  rv.b = 'str';
  return rv;
}

I expect the tsc to throw errors that at least the a property is missing on the returned value of type Foo. But this doesn't happen. If I use the line: const rv = { }; then it throws, but about both of the props: a and b, which is better.

But why doesn't it throw with the Object.create(null)?

It doesn't matter if I use the Required<> type or not.

Answer 1

Let's look at Object.create() official definition:

    /**
     * Creates an object that has the specified prototype or that has null prototype.
     * @param o Object to use as a prototype. May be null.
     */
    create(o: object | null): any;

    /**
     * Creates an object that has the specified prototype, and that optionally contains specified properties.
     * @param o Object to use as a prototype. May be null
     * @param properties JavaScript object that contains one or more property descriptors.
     */
    create(o: object | null, properties: PropertyDescriptorMap & ThisType<any>): any;

As we can see, it has two overloadings, both accepting object | null. That's why you don't get the error when passing null. Both of the overloadings return any, so setting the property also doesn't fire any error.