calculating 2+ form field inputs on the fly
I'm working on a financial form that is filled out and then a pdf is outputted (via php).
I've got a section for "project costs" with 4 fields (numeric is expected). I'd like to add a 5th field "Total Project Cost" that adds all the inputs of the first 4 fields on the fly as they are typed (or at least, after focus changes).
Also I'd like to have a field which defaults to "10" and a drop down with 3 items that will either add 0, 5 or 10 to the field which defaults to 10.
Can anyone recommend a script or js library that can handle these "on the fly" calculations? I appreciate the help - Thank you! :)