Concatenate values from two text box and populate the value in another text box

Today I had to create a function to concatenate two values from a text box and populate the output in another text box. This I did to inmprove the usability of the form for inputing the credit card data.

This is what I wrote



function conc()
{
var mon;
var yy;

yy=document.getElementById("Texty").value;
mon=document.getElementById("Textm").value;
document.getElementById("Texte").value=yy+mon;
}