How to display sum of two TextBoxes in third TextBox using JavaScript

first of all convert the value of cost salary and cost ahead into the integer .

and add it.

like that in java script

document.getElementById('totalcost').value=total;

var salary=document.getElementById('cost salary').value;

var ahead=document.getElementById('cost ahead').value;

var total=parseInt(salary)+parseInt(ahead);

after that set the value in total like that

document.getElementById('totalcost').value=total;