spread doesn't mutate

spread.js

var foo = { a: 1, b: 2 };
var bar = foo;

bar.c = 3;
console.log(bar); //=> { a:1, b:2, c:3 }
console.log(foo); //=> { a:1, b:2, c:3 } foo was mutated

//however

foo = { a: 1, b: 2};
var baz = {...foo};
baz.c = 3;

console.log(baz); //=> { a:1, b:2, c:3 }
console.log(foo); //=> { a:1, b:2 } foo wasn't mutated