Javascript – insert an array inside another array

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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);

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