JS: use spread to exclude properties

I thought I'd share this small trick with you because I find myself looking this up every now and then when I need it.

The spread operator in JavaScript can be very useful.
For example to create a copy of an object:

const firstObject = {id: 0, name: 'John'};
const secondObject = {...firstObject};

console.log(firstObject);
console.log(secondObject);

// { id: 0, name: 'John'}
// { id: 0, name: 'John'}

But did you know you can also use it to except properties when spreading?

const firstObject = {id: 0, firstName: 'John', lastName: 'Smith', age: 77 };
// take every property except age:
const {age, ...secondObject} = firstObject;

console.log(firstObject);
console.log(secondObject);
// { id: 0, firstName: 'John', lastName: 'Smith', age: 77 }
// { id: 0, firstName: 'John', lastName: 'Smith' }

The above example will extract age as own variable and will put the remaining in the object secondObject. You can do that with as many properties as you want.

Comments

[Michael Schinis]

Although the gist of the above is correct, the right hand side of the following code creates a copy of the firstObject before extracting age, and creating secondObject, allocating more memory unnecessarily.

const {age, ...secondObject} = {...firstObject};

The following achieves the same outcome, but skips the extra allocation.

const {age, ...secondObject} = firstObject

[Robin Kretzschmar]

Thank you for the explanation, you are absolutely correct about this. That was is more efficient 👍

[Marc Selman]

You might wanna update your original post for people who don't read the comments. 😉

[Robin Kretzschmar]

Good catch, thanks!
Lost track of it, updated :)

[Erick]

THANK YOU SO MUCH ;)

[essofyany]

thanks bro <3