/this-vs-that GitHub 1316★

Object.getOwnPropertyNames() vs Object.keys()


  1. Object.getOwnPropertyNames(obj) returns all the properties of the object obj. Object.keys(obj) returns all enumerable properties.

    They provide the same result unless you set enumerable: false to any property.

    In the following example, the screen object has two properties, branch and size.

    const screen = {
    branch: 'Dell',
    size: '27inch',

    Object.getOwnPropertyNames(screen); // ['branch', 'size']
    Object.keys(screen); // ['branch', 'size']

    Let's define one more property named resolution but it is set as enumerable: false:

    Object.defineProperties(screen, {
    resolution: {
    enumerable: false,
    value: '2560 x 1440',

    The resolution property then doesn't appear in the list of Object.keys:

    Object.getOwnPropertyNames(screen); // ['branch', 'size', 'resolution']
    Object.keys(screen); // ['branch', 'size']
  2. For arrays, Object.getOwnPropertyNames includes an extra property named length which is the size of the array.

    const animals = ['dog', 'cat', 'tiger'];

    Object.keys(animals); // ['0', '1', '2']
    Object.getOwnPropertyNames(animals); // ['0', '1', '2', 'length']
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