Javascript: push an entire list?

Question

Is there a built in way to append one list into another like so:

var a = [1,2,3];
a.append([4,5]);
// now a is [1,2,3,4,5];

concat() does something similar but returns the result. I want something that modifies the existing list like push()

Answer 1

push will work, but you also need to use apply.

var a = [1,2,3];
a.push.apply(a, [4,5])

Answer 2

var list = [1, 2];

People already showed you how to do this with:

1. push: list.push.apply(list, [3, 4]);
2. concat: list = list.concat([4, 5]);

But I want to tell about ES6 spread operator: list.push(...[3, 4]);.

Keep in mind that currently not many browsers support it (you can use transpilers).