Difference between Object.assign and object spread

Question

Having

var obj = { a: 1, b: 2};

What are the differences between

obj = Object.assign(obj, { c: 3});

And

obj = {...obj,  c: 3 };

Answer 1

The difference is that when using a spread you are always creating a new object:

const a = { name: 'Joe Bloggs' }
const b = { ...a, age: 27 };

console.log(a === b) //=> false

However using Object.assign it is possible to mutate an existing object:

const a = { name: 'Joe Bloggs' }
const b = Object.assign(a, { age: 27 });

console.log(a === b) //=> true

You still can achieve the behaviour of an object spread with Object.assign by passing an empty object literal as the first argument:

const a = { name: 'Joe Bloggs' }
const b = Object.assign({}, a, { age: 27 });

console.log(a === b) //=> false