how add an elenent a specific position in array in javascript code example

Example 1: javascript push in specific index

arr.splice(index, 0, item);
//explanation:
inserts "item" at the specified "index",
deleting 0 other items before it

Example 2: array insertion javascript

Array.prototype.insert = function ( index, item ) {
    this.splice( index, 0, item );
};