lib.d.ts Make Object.keys generic

[mohsen1]

TypeScript Version: 2.5

Currently Object.keys type is keys<T>(o: {}): string[]; but instead it can be keys<T = {}>(o: T): keyof T; so return type is a union of keys.

Any reason this hasn't been done before? I can make a PR if this is an acceptable change

[mhegazy]

Please see #15627

[mohsen1]

This comment
#12253 (comment)

But I'm not convinced. We either have strong typing or not. if someone is depending on runtime data without statically declaring them it is their problem and can case the types to a wide type

/cc @ahejlsberg

Closing as it is by design

[kitsonk]

If someone is depending on runtime data without statically declaring them it is their problem.

At the moment, TypeScript does not differentiate between own keys and enumerable keys, both which are not covered by Object.keys(). So there is a lot of ways, intentionally or unintentionally Object.keys() typed as suggested would give back bad information.

For example, it breaksdown badly here:

const foo = Object.create({ foo: 'string' });
Object.defineProperty(foo, 'bar', {
  value: 1
});

console.log(Object.keys(foo)); // []
console.log(foo.foo); // 'string'
console.log(foo.bar); // 1

Sounds like a bad 👣 🔫 to me...