Is there an immutable version of Object.assign?

Question

I want to mix two objects in JavaScript:

let a = {x: 1, y: 2, z:3};
let b = {x:10, y: 20};

let c = Object.assign(a, b);

This gives the correct value for c:

Object { x: 10, y: 20, z: 3 }

But now a has been modified too!

Object { x: 10, y: 20, z: 3 }

Is there a way to assign a onto b into a new object?

Answer 1

The first argument to assign is the target. So it's going to get changed. You can simply pass an empty object for your target if you don't want any of the sources to change:

let a = {x: 1, y: 2, z:3};
let b = {x:10, y: 20};

let c = Object.assign({},a, b);
console.log(c);
console.log(a);    // a is unchanged

Answer 2

You could use the spread operator:

let a = {x: 1, y: 2, z: 3};
let b = {x: 10, y: 20};

let c = {
  ...a,
  ...b
}

console.log(c);
console.log(a);