How to spread an object into a classes properties in JavaScript

Question

Basically here's what I'm trying to accomplish.

class Person {
  constructor (obj) {
    this.first = ''
    this.last = ''
    this.age = ''

    if (obj) {
      Object.assign(this, ...obj)
    }
  }
}

const a = new Person()
console.log('Not spreading: ', a)

const b = new Person({ first: 'Alex', last: 'Cory', age: 27 })
console.log('Spreading: ', b)

Is there a way to spread an object like this to populate a class?

Answer 1

If you're using Object.assign, you don't use spread notation; just remove the ...:

class Person {
  constructor (obj) {
    this.first = ''
    this.last = ''
    this.age = ''

    if (obj) {
      Object.assign(this, obj)     // <============ No ...
    }
  }
}

const a = new Person()
console.log('Not spreading: ', a)

const b = new Person({ first: 'Alex', last: 'Cory', age: 27 })
console.log('Spreading: ', b)

There is a proposal (currently at Stage 3, so likely to be in ES2018, and widely supported by transpilers) that does object property spread in object initializers, but that wouldn't apply to your situation where the object already exists.