[Solved] How expand (open) a DropDownList on mouse over focus using JavaScript

Hello everyone I want to expand dropdownlist when focus goes to it. I am using this code

 function Open() {
            var myDropDown = document.getElementById("myDropDown");
            var length = myDropDown.options.length;            
            myDropDown.size = length;   
        }

But the problem with this code is that it converts the dropdown to listbox, I want to expand it only.

Please help