How would I set up a method to update passed properties of JavaScript object?

Question

I'm looking to create a method for an object to update only the properties that are passed.

for example

function Car () {
  this.color = 'yellow'
  this.brand = 'bmw'
  this.key = 0

  this.update = function (o) {
    this.key++
    // maybe Object.assign(this, o) somehow ??
  }
}

If I do Car.update({color:'red'}) I want to update the object but not overwrite the brand. I want to use something like Object.assign(this, o) but not sure how to assign it. Do I need to create a prototype? Car.prototype.update = ?

So what went wrong with Object.assign? It will update this if you pass that as first argument. No need to assign anything more. — trincot
– trincot, Commented Nov 11, 2018 at 21:08
but i would have to assign it to something right? like this = Object.assign(this, o) but that's a no-go — Olgo
– Olgo, Commented Nov 11, 2018 at 21:24
@trincot Ah, i see. looking at the docs, i didn't realize it copies to the first parameter which is the target. I thought it had to return something which you would then save to a var. convert that to an answer. :) — Olgo
– Olgo, Commented Nov 11, 2018 at 21:35

M. L. · Accepted Answer · 2018-11-11 21:40:52Z

1

The idea you suggested in your OP works fine.

function Car () {
  this.color = 'yellow';
  this.brand = 'bmw';
  this.key = 0;

  this.update = function (o) {
	Object.assign(this, o);
  }
}

a = new Car();
a.update({color: "red"});
console.log(a.color + " - " + a.brand + " - " + a.key);
// returns "red - bmw - 0"

answered Nov 11, 2018 at 21:40

M. L.

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trincot · Accepted Answer · 2018-11-11 21:41:57Z

0

Object.assign mutates the first argument, so there is no need to assign the result of Object.assign() to something.

Object.assign(this, o);

...will work fine.

function Car () {
  this.color = 'yellow'
  this.brand = 'bmw'
  this.key = 0

  this.update = function (o) {
    this.key++
    Object.assign(this, o);
  }
}

var car = new Car();
car.update({color: 'red'});
console.log(car);

answered Nov 11, 2018 at 21:41

trincot

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Nattamai Jawaharlal Manikandan · Accepted Answer · 2018-11-11 21:12:28Z

0

const object1 = {
color : 'red'
};

const obj2 = Object.assign({color: 'blue', d: 5}, object1);
console.log(obj2.color); // red

Object.assign() method -> copy the values of all enumerable own properties. Finally It will return the target object

answered Nov 11, 2018 at 21:12

Nattamai Jawaharlal Manikandan

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1 Comment

Olgo Over a year ago

I just wanted it to be in a method, to keep it clean and so i can tie other functionality to it whenever there is an update, i updated my question to show what else I would like to tie in. to give a better idea of what i'm trying to accomplish

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