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Object.getOwnPropertyNames() vs Object.keys()

Written byPhuoc Nguyen
10 Jun, 2020


  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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