I'm sure this is basic stuff but I'd like any text input that's left blank to have a value of zero so it can still be included in a function and not mess with the final sum of the equation. 

At the moment I'm just setting `<input type="text" id="id" value="0">` since nothing will be divided by a `var value = document.getElementById("id");` but I don't want to see the zeros in the text boxes.

Is there an better way to not include empty inputs in an equation?