The Object getOwnPropertyDescriptors() method

Find out all about the JavaScript getOwnPropertyDescriptors() method of the Object object

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This method returns all own (non-inherited) properties descriptors of an object.

Object.getOwnPropertyDescriptors(obj) accepts an object, and returns a new object that provides a list of the descriptors.

Example:

const dog = {}
Object.defineProperties(dog, {
  breed: {
    value: 'Siberian Husky'
  }
})
Object.getOwnPropertyDescriptors(dog)
/*
{
  breed: {
    value: 'Siberian Husky',
    writable: false,
    enumerable: false,
    configurable: false
  }
}
*/

There is one use case that makes this property very useful. ES2015 gave us Object.assign(), which copies all enumerable own properties from one or more objects, and return a new object. However there is a problem with that, because it does not correctly copies properties with non-default attributes.

If an object for example has just a setter, it’s not correctly copied to a new object, using Object.assign(). For example with this object:

const person1 = {
  set name(newName) {
    console.log(newName)
  }
}

This copy attempt won’t work:

const person2 = {}
Object.assign(person2, person1)

But this will work and copy over the setter correctly:

const person3 = {}
Object.defineProperties(person3,
  Object.getOwnPropertyDescriptors(person1))

As you can see with a console test:

person1.name = 'x'
"x"

person2.name = 'x'

person3.name = 'x'
"x"

person2 misses the setter, it was not copied over.

The same limitation goes for shallow cloning objects with Object.create().

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