How to insert an item into an array at a specific index javascript

var arr = ["X1", "X2", "X3", "X4", "X5"];

Inserting "X2.2" into position "2" without deleting "0" item
arr.splice(2, 0, "X2.2");

First Array Values:
X1,   X2,   X3,   X4,   X5

After insert new value:
X1,   X2,   X2.2,   X3,   X4,   X5