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Automatically adjust numbers in input fields to match max value


I got a very specific and interesting task, but i'm not sure where to begin, but very excited to get started :)
I have been working on an online Cylinder Configurator for the company I work in and everything has been working fine so far, but the next part is a bit tricky and i'm not sure where to start.

Please see attached PDF sketch.

- I need to place 4 input fields on top of an image-background, this is no problem.

Here is my problem:
- If "A" is changed, then "D" need to be adjusted accordingly.
- If "B" is changed, then "D" need to be adjusted accordingly.
- If "C" is changed, then "D" need to be adjusted accordingly.
- If "D" is changed, then "A" need to be adjusted accordingly.

Any idea how this is normally done? I would prefer to use some kind of "live updating" solution, without a "page load".


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1 Solution
Simplistic example of how to bind the recalculation to whenever any of the inputs change.
In the example I hard coded the new value for A and D.  Obviously, you'll want to use your real formula instead.  Also, this example does not do anything to ensure that the values in the input fields are numeric, you'll probably want to add that in too.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
	<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
	<script src="http://code.jquery.com/jquery-latest.min.js" type="text/javascript"></script>
function recalcInputs(element) {
  if ($(element).attr('name') == 'd') {
    //math to recalculate a goes here
    newAvalue = 12;
  } else {
    //math to recalculate d goes here
    newDvalue = 77;

A: <input name="a" value="" type="text" onblur="javascript:recalcInputs(this)"><br/>
B: <input name="b" value="" type="text" onblur="javascript:recalcInputs(this)"><br/>
C: <input name="c" value="" type="text" onblur="javascript:recalcInputs(this)"><br/>
D: <input name="d" value="" type="text" onblur="javascript:recalcInputs(this)"><br/>

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Ray PaseurCommented:
This is the perfect task for AngularJS!
kgp43Author Commented:
Going to look into that, exactly what i'm looking for it seems.
Ray PaseurCommented:
I've been using AngularJS for about a month, still just stumbling along at this point.  It mixes the declarative notation of HTML with the imperative structure of a programming language.  And while I think it's a laudable effort to turn a silk purse into a sow's ear, the next "real" solution for online web applications is probably still out in the future, and is probably not back-level compatible with JavaScript and HTML.  That aside, AngularJS is a really big step in the right direction!

Thanks for the points and best of luck with your project! ~Ray
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