Edit in JSFiddle

console.error("***** adding single element 'drum' at index 2 *****");
var myFish = ['angel', 'clown', 'mandarin', 'sturgeon'];
myFish.splice(2, 0, 'drum');
console.log('myFish is', myFish);
// myFish is ["angel", "clown", "drum", "mandarin", "sturgeon"] 


console.error("***** adding 'drum' and 'guitar' at index 2 *****");
myFish = ['angel', 'clown', 'mandarin', 'sturgeon'];
myFish.splice(2, 0, 'drum', 'guitar');
console.log('myFish is', myFish);
// myFish is ["angel", "clown", "drum", "guitar", "mandarin", "sturgeon"]