kamilkp kamilkp - 5 months ago 41
Javascript Question

Object.getOwnPropertyNames vs Object.keys

What's the difference between

Object.getOwnPropertyNames
and
Object.keys
in javascript? Also some examples would be appreciated.

Answer

There is a little difference. Object.getOwnPropertyNames(a) returns all own properties of the object a. Object.keys(a) returns all enumerable own properties. It means that if you define your object properties without making some of them enumerable: false these two methods will give you the same result.

It's easy to test:

var a = {};
Object.defineProperties(a, {
    one: {enumerable: true, value: 'one'},
    two: {enumerable: false, value: 'two'},
});
Object.keys(a); // ["one"]
Object.getOwnPropertyNames(a); // ["one", "two"]

If you define a property without providing property attributes descriptor (meaning you don't use Object.defineProperties), for example:

a.test = 21;

then such property becomes an enumerable automatically and both methods produce the same array.

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