What is the difference between Reflect.ownKeys(obj) and Object.keys(obj)?

Question

Testing them out in a real simple case yields the same output:

const obj = {a: 5, b: 5};
console.log(Reflect.ownKeys(obj));
console.log(Object.keys(obj));

// Re         


        

Answer 1

First, an example (ES6Fiddle):

// getFoo is property which isn't enumerable
var my_obj = Object.create({}, { getFoo: { value: function() { return this.foo; } } });
my_obj.foo = 1;

console.log(Object.keys(my_obj)); // console ['foo']
console.log(Reflect.ownKeys(my_obj)); // console ['getFoo', 'foo']

Here, Reflect.ownKeys() returns an array of the target object's own property keys. Namely, an array of all properties (enumerable or not) found directly upon the given object concatenated with an array of all symbol properties found directly upon the given object.

Object.keys() will only return the enumerable properties.

Enumerable properties are those that can be enumerated by a for...in loop, with the exception of properties inherited through the prototype chain. See the MDN description for more details.

Summary:

Reflect.ownKeys() is the equivalent of Object.getOwnPropertyNames(target).concat(Object.getOwnPropertySymbols(target)) which will return both enumerable and non-enumerable properties

whereas

Object.keys() returns enumerable properties but does not return non-enumerable properties (which is a characteristic of Object.getOwnPropertyNames()).