selectbox value calculation - php

Question

I want to do a calculation between selectbox values. The problem with my code is that the first part of the calculation only gives me 0, which Motherboard valuequantity. the second part works fine which Chassisquantity. My formulas is motherbord*Quanity+chassis*quantity.
Here is my code:
function calculate() {
var parsedMotherboard = parseFloat(document.calcform.Motherboard.value || 0);
var parsedQuantity = parseFloat(document.calcform.Quantity.value || 0);
var parsedChassis = parseFloat(document.calcform.Chassis.value || 0);
var parsedQuantity1 = parseFloat(document.calcform.Quantity1.value || 0);
document.calcform.total.value = (parsedMotherboard * parsedQuantity + parsedChassis * parsedQuantity1);
}

Answer 1

It helps if you format your code more neatly:
function calculate() {
var parsedMotherboard = parseFloat(document.calcform.Motherboard.value || 0);
var parsedQuantity = parseFloat(document.calcform.Quantity.value || 0);
var parsedChassis = parseFloat(document.calcform.Chassis.value || 0);
var parsedQuantity1 = parseFloat(document.calcform.Quantity1.value || 0);
document.calcform.total.value = (parsedMotherboard * parsedQuantity +
parsedChassis * parsedQuantity1);
}
Have you checked that you are getting the correct values from the form? Make sure that the default option (I'm assuming the first one with a value of 0) has the selected attribute set so that one option is always selected.
Some other tips:
store a reference to the form, it's more efficient and makes for neater code
Since you set the value, you know it's formatted correctly so rather than using parseInt, just use the uary + operator to convert to number
Personal preference, but use shorter variable names so they're easier to work with
I don't understand the need for || 0. If the user doesn't select something, isn't the default value 0?
Here is an updated version:
function calculate() {
var form = document.calcform;
var mb = +form.Motherboard.value;
var mbQty = +form.Quantity.value;
var ch = form.Chassis.value;
var chQty = form.Quantity1.value;
form.total.value = mb*mbQty + ch*chQty;
}
Because each string value is involved in a multiplication, there is no need to explicitly convert to number, that will happen as a consequence of the multiplication, so you could write:
function calculate() {
var form = document.calcform;
form.total.value = form.Motherboard.value * form.Quantity.value +
form.Chassis.value * form.Quantity1.value;
}

Answer 2

do it with jQuery ...
$('#selectbox1').change(function() {
// do ajax if you want or store
var x = $('#selectbox1').attr('value'); // or you can use this.value
// and so on
});
and sum up the other selectboxes