module.exports = insert;

/*

insert([1, 2, 5, 6], ['a', 'c', 'e'], 2); // [1, 2, 'a', 'c', 'e', 5, 6]

insert([1, 2, 5, 6], 'a', 2); // [1, 2, 'a', 5, 6]

insert([1, 2, 5, 6], ['a', 'c', 'e'], 0); // ['a', 'c', 'e', 1, 2, 5, 6]

insert([1, 2, 5, 6], ['a', 'c', 'e']); // ['a', 'c', 'e', 1, 2, 5, 6]

*/

function insert(arr1, arr2, index) {

if (!Array.isArray(arr1)) {

throw new Error('expected an array for first argument');

}

if (arguments.length > 2 && typeof index != 'number') {

throw new Error('expected a number for third argument');

}

if (!Array.isArray(arr2)) {

arr2 = [arr2];

}

if (!index) {

return arr2.concat(arr1);

}

var front = arr1.slice(0, index);

var back = arr1.slice(index);

return front.concat(arr2, back);

}