array.splice(start, deleteCount[, item1[, item2[, ...]]])

var arr = new Array("4", "11", "2", "10", "3", "1");
arr.splice(2, 2, "21", "31");
document.write(arr);

// Output: 4,11,21,31,3,1

var myFish = ['angel', 'clown', 'mandarin', 'surgeon'];

// removes 0 elements from index 2, and inserts 'drum'
var removed = myFish.splice(2, 0, 'drum');
// myFish is ['angel', 'clown', 'drum', 'mandarin', 'surgeon']
// removed is [], no elements removed

// removes 1 element from index 3
removed = myFish.splice(3, 1);
// myFish is ['angel', 'clown', 'drum', 'surgeon']
// removed is ['mandarin']