Calculation on vTiger field before save handler on Javascript Side (code inside)

I need to understand how to do real time calculation on Edit.js

By searching and looking around i came up with this code in Edit.js of the Contact Module.

calculate_amount: function (){
var units = $("input[name='cf_852']");
var value = $("input[name='cf_854']");
$(units, value).on('keyup', function(){
if (units.val() != '' && value.val() != ''){
var currentamount = units.val() * value.val();
$("input[name='cf_856']").val(currentamount);
}
});
}

Have i done something wrong? Because it doesn't work..

Thanks for all the help!

I should write your keyup function like this:

I tested, it's OK

calculateAmount: function (){  
  var units = $("input[name='cf_1512']");
  var value = $("input[name='cf_1514']");
  $(document).on('keyup',"input[name='cf_1512'], input[name='cf_1514']", function(){
    if (units.val() != '' && value.val() != ''){
      var currentamount = units.val() * value.val();
      $("input[name='cf_1518']").val(currentamount);
    }
  })
},