How do you add Form Field values together before the form is submitted

[kpetsche20]

I have a form, it allows a person to add 3 products, each form has a different value. I want to add those values together before the form submits.

[F1Fan]

In your JS validation function, add the values together and put the sum in a hidden input.

[kpetsche20]

I'm pretty new to JS I don't know what to code and where to put it.

[PFMaBiSmAd]

I would do any addition on the server in the form processing code. If you are adding numbers in the browser and you are depending on the value to be accurate, you will find that there are a lot of people who would submit incorrect information in order to pay a lower price for something or to cheat at games....

[kpetsche20]

I have php code setup to detect fraudulent users, I just want it as a convenience factor for signups

[F1Fan]

JS:

function validateForm(){
  var val1 = parseInt(document.getElementById('firstinput').value,10);
  var val2 = parseInt(document.getElementById('secondinput').value,10);
  var val3 = val1+val2;
  document.getElementById('thirdinput').value = val3;
}

HTML:

<input type="text" name="firstinput" id="firstinput">
<input type="text" name="secondinput" id="secondinput">
<input type="hidden" name="thirdinput" id="thirdinput">
<input type="submit" value="Submit" onclick="return validateForm();">