JSFiddle - React, Tailwind, and code Playground

HTML

<p>jQuery programm with the
    <a href="http://en.wikipedia.org/wiki/Reactive_programming">
        Reactive programming concept</a>
</p>
<p>X = <span id="X" title="click here">22</span></p>
<p>Y = <span id="Y" title="click here">33</span></p>
<p>A = X+Y = <span id="A"></span> -- click the red boxes</p>

CSS

#Y,#X {background-color:#FAA}
#A {background-color:#AAF}

JavaScript

function setA(){  // A=X+Y as integers
    var A = parseInt($('#X').text()) + parseInt($('#Y').text());
    $('#A').text( A );
 }

 setA();
 $('#X,#Y').css('cursor','pointer').click(function(){
    // by reaction to a click: updates A and X or Y
    var obj = $(this);
    obj.text(parseInt(obj.text())+1);
    setA();
 });

 //ppkrauss