how to destruct part of properties from an object

Question

For example, I got an object like this:

obj1 = {
     name: 'Bob',
     age:  20,
     career: 'teacher'
  }

Now I need to duplicate part of its properties instead all of them.

obj2 = {
     name: '',
     age: '',
  }

I know I can do it like obj2.name = obj1.name, which will be verbose if many properties need to be duplicated. Are there any other quick ways to solve this problem? I tried

let {name: obj2.name, age: obj2.age} = obj1;

but got error.

you could use a white list for properties, or a black list. then iterate. — Nina Scholz, Sep 04 '17 at 09:21
take a look at [this](https://stackoverflow.com/questions/728360/how-do-i-correctly-clone-a-javascript-object) — Max, Sep 04 '17 at 09:26
Take a look at [One-liner to take some properties from object in ES6](https://stackoverflow.com/q/25553910/1048572) — Bergi, Sep 04 '17 at 09:30

Jonathan · Accepted Answer · 2017-09-04T09:43:33.020

6

Actually you don't need object destructuring, just simple assignment:

obj2 = { name: obj1.name, age: obj1.age }

Now, obj2 holds wanted properties:

console.log(obj2);
// Prints {name: "Bob", age: 20}

If you want to merge old properties of obj2 with new ones, you could do:

obj2 = { ...obj2, name: obj1.name, age: obj1.age }

edited Sep 04 '17 at 09:43

answered Sep 04 '17 at 09:23

Jonathan

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score 1 · Answer 2 · answered Sep 04 '17 at 09:26

1

Drop the let (you're not declaring variables) and surround with parentheses:

({name: obj2.name, age: obj2.age} = obj1);

answered Sep 04 '17 at 09:26

Bergi

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Your code doesn't work, it should be `(obj1 = {name: obj2.name, age: obj2.age});` – alexmac Sep 04 '17 at 09:32
It works! Would you please explain why or what the parentheses did. – xiaojie Luo Sep 04 '17 at 09:33
@Bellian It's destructuring without `let` – Bergi Sep 04 '17 at 09:34
@xiaojieLuo See the link that explains why the parentheses are necessary – Bergi Sep 04 '17 at 09:34
I see. I forgot to init the obj2. that makes sense! – Bellian Sep 04 '17 at 09:35
@Bergi no, it doesn't [https://jsfiddle.net/m9692mg6/1/](https://jsfiddle.net/m9692mg6/1/) – alexmac Sep 04 '17 at 09:38

score 0 · Answer 3 · answered Sep 04 '17 at 09:31

0

I guess you can use ES6 Object destructuring syntax

   var obj = { name: 'kailash', age: 25, des: 'backenddev'}
   ({name} = obj);

answered Sep 04 '17 at 09:31

kailash yogeshwar

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That assigns to a global `name` variable? – Bergi Sep 04 '17 at 09:35
yeah it does assign to global name var – kailash yogeshwar Sep 04 '17 at 09:45
Yes - don't do that :-) – Bergi Sep 04 '17 at 09:46
I thought obj destructing was as similar to array but it isn't. – kailash yogeshwar Sep 04 '17 at 09:47

score 0 · Answer 4 · answered Sep 04 '17 at 10:05

You could use the target object as template for the properties and assign the values of obj1 with a default value of the target object.

var obj1 = { name: 'Bob', age:  20, career: 'teacher' },
    obj2 = { name: '', age: '' };
    
Object.keys(obj2).forEach(k => obj2[k] = obj1[k] || obj2[k]);

console.log(obj2);

score 0 · Answer 5 · answered Sep 04 '17 at 12:52

Another solution would be to write a reuable method for this. You can supply an object and the methods you would like to copy.

const duplicatePropertiesFromObject = (obj, propertyNames = [], newObj = {}) => {
  Object.keys(obj).forEach((key) => {
    if (propertyNames.includes(key)) {
      newObj[key] = obj[key];
    }
  });
  return newObj;
}

how to destruct part of properties from an object

5 Answers5