The Object keys() method

Apr 12, 2019

Learn how the JavaScript Object.keys() method returns an array of an object own enumerable property names, and how to use it with reduce to copy an object.

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Object.keys() accepts an object as argument and returns an array of all its (own) enumerable properties.

const car = {
  color: 'Blue',
  brand: 'Ford',
  model: 'Fiesta'
}

Object.keys(car) //[ 'color', 'brand', 'model' ]

I said enumerable properties. This means their internal enumerable flag is set to true, which is the default. Check MDN for more info on this subject.

One use of the Object.keys function is to create a copy of an object that has all the properties of it, except one:

const car = {
  color: 'blue',
  brand: 'Ford'
}
const prop = 'color'

const newCar = Object.keys(car).reduce((object, key) => {
  if (key !== prop) {
    object[key] = car[key]
  }
  return object
}, {})

Tagged: JavaScript · All topics

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