Javascript - insert an array inside another array

Question

What is the more efficient way to insert an array inside another array.

a1 = [1,2,3,4,5]; a2 = [21,22];  newArray - a1.insertAt(2,a2) -> [1,2, 21,22, 3,4,5]; 

Iterating a2 using splice looks a bit awfull from a performance point of view if a2 array is large.

Thanks.

Answer 1

You can use splice combined with some apply trickery:

a1 = [1,2,3,4,5]; a2 = [21,22];  a1.splice.apply(a1, [2, 0].concat(a2));  console.log(a1); // [1, 2, 21, 22, 3, 4, 5]; 

In ES2015+, you could use the spread operator instead to make this a bit nicer

a1.splice(2, 0, ...a2);