Javascript - copy object using keys from array

Question

I have an array with names in.

I also have an object with keys that are the same as those in the array. The object also has other keys.

I would like to copy the object but only include the keys that are in the array

const keys = ['one', 'two', 'three'];

const obj = {
 date: 'Jan',
 color: 'Red',
 one: 367,
 two: 427,
 three: 753
}

const objCopy = Object.assign({}, obj)


// I'd like this console to display
// {
//   "one": 367,
//   "two": 427,
//   "three": 753
// }

console.log(objCopy)

[Filter object properties by key in ES6](https://stackoverflow.com/questions/38750705/filter-object-properties-by-key-in-es6) — Alona, Jun 18 '19 at 08:21

score 4 · Answer 1 · answered Jun 18 '19 at 08:10

Very simple reduce.

const keys = ['one', 'two', 'three'];

const obj = {
  date: 'Jan',
  color: 'Red',
  one: 367,
  two: 427,
  three: 753
};

const res = keys.reduce((a, c) => (obj[c] ? a[c] = obj[c] : c, a), {});
console.log(res);

(The ternary operator ensures that the key actually exists in the object - otherwise you'd get undefineds in your result that you'd have to filter out).

score 3 · Accepted Answer · answered Jun 18 '19 at 08:09

3

const keys = ['one', 'two', 'three'];

const obj = {
 date: 'Jan',
 color: 'Red',
 one: 367,
 two: 427,
 three: 753
}

const objCopy = {};

keys.forEach(key => objCopy[key] = obj[key]);

console.log(objCopy)

answered Jun 18 '19 at 08:09

George Wang

451
2
12

score 2 · Answer 3 · answered Jun 18 '19 at 08:07

2

Using forEach loop

const keys = ['one', 'two', 'three'];

const obj = {
 date: 'Jan',
 color: 'Red',
 one: 367,
 two: 427,
 three: 753
}
var obj1={};
keys.forEach(e=>{
obj1[e]=obj[e]
})
const objCopy = Object.assign({}, obj1)
console.log(objCopy)

answered Jun 18 '19 at 08:07

ellipsis

12,049
2
17
33

score 2 · Answer 4 · answered Jun 18 '19 at 08:15

It is possible to get the desired object using the following way:

const keys = ['one', 'two', 'three'];

const obj = {
    date: 'Jan',
    color: 'Red',
    one: 367,
    two: 427,
    three: 753
}

let desiredObject = Object.keys(obj)
    .filter(key => keys.includes(key))
    .map(key => {
        return {[key]: obj[key]}
    })
    .reduce((a, b) => Object.assign({}, a,b));

score 1 · Answer 5 · answered Jun 18 '19 at 08:06

This might help you, you have to loop through the keys array and add grab every existing key from obj in order to construct your new object. Which is not a copy, it's a new object with your desired keys.

const keys = ['one', 'two', 'three'];

const obj = {
 date: 'Jan',
 color: 'Red',
 one: 367,
 two: 427,
 three: 753
}

const objCopy = {};

for (let i = 0; i < keys.length; i++) {
  objCopy[keys[i]] = obj[keys[i]];
}

console.log(objCopy)

You don't need to use any other fancy methods to do this, other methods will indeed reduce the number of the code lines but will decrease your performance, like using .reduce() or other Array methods.

score 1 · Answer 6 · answered Jun 18 '19 at 08:07

You can use .reduce on the keys array to get the desired object.

const keys = ['one', 'two', 'three'];

const obj = {
 date: 'Jan',
 color: 'Red',
 one: 367,
 two: 427,
 three: 753
}

const objCopy = keys.reduce((a,e) => {
  a[e] = obj[e];
  return a;
}, {});

console.log(objCopy)

score 1 · Answer 7 · answered Jun 18 '19 at 08:08

1

cont objCopy = Object.entries(obj).reduce(([key, value],acc)=>keys.includes(key)?{...acc, key:value}:acc, {})

answered Jun 18 '19 at 08:08

Will Jenkins

9,507
1
27
46

score 1 · Answer 8 · edited Jun 18 '19 at 08:30

1

The hasOwnProperty is used to exclude inherited properties

const keys = ['one', 'two', 'three'];

const obj = {
  date: 'Jan',
  color: 'Red',
  one: 367,
  two: 427,
  three: 753
}

const objCopy = {}; // copy

for (let property in obj) {
  if (obj.hasOwnProperty(property) && keys.find(k => k == property)) {
    objCopy[property] = obj[property];
  }
}

console.log(objCopy);

edited Jun 18 '19 at 08:30

codeherk

1,609
15
24

answered Jun 18 '19 at 08:09

LiefdeWen

586
2
14

+1 for checking if it has the property. I suggested an edit to have `let` inside for loop. we should use `let` and `const` in JS and retire use of `var` – codeherk Jun 18 '19 at 08:11
1

First your code is wrong - duplicated `obj` declaration. And for `object` - it's better to use `const` than `let` if you don't need assignment another value. – Alona Jun 18 '19 at 08:13
1

@АленаВерещака I addressed your concerns – LiefdeWen Jun 18 '19 at 08:27

score 1 · Answer 9 · answered Jun 18 '19 at 08:10

1

Try this:

const obj = {
 date: 'Jan',
 color: 'Red',
 one: 367,
 two: 427,
 three: 753
}

const extract = ({one, two, three}) =>Object.assign({},{one, two, three});

console.log(extract(obj))

answered Jun 18 '19 at 08:10

Ghoul Ahmed

4,446
1
14
23

1

It's not the answer for this Question. If you need additional property `four` then how much do you need to update? – Alona Jun 18 '19 at 08:15
1

@АленаВерещака ,add in params , ({, four}) , i use destructuring objects as function parameters in ES6..., this is solution without using any iterations (foreach, map ...) – Ghoul Ahmed Jun 18 '19 at 08:21
1

Ahmen, thanks for your reply. I think the point of question is asking how to copy object by filtering `key` array which consist `string` keys inside. Thanks – Alona Jun 18 '19 at 08:24

Javascript - copy object using keys from array

9 Answers9