Firing events on CSS class changes in jQuery

Whenever you change a class in your script, you could use a trigger to raise your own event.

$(this).addClass('someClass');
$(mySelector).trigger('cssClassChanged')
....
$(otherSelector).bind('cssClassChanged', data, function(){ do stuff });

but otherwise, no, there's no baked-in way to fire an event when a class changes. change() only fires after focus leaves an input whose input has been altered.

$(function() {
  var button = $('.clickme')
      , box = $('.box')
  ;
  
  button.on('click', function() { 
    box.removeClass('box');
    $(document).trigger('buttonClick');
  });
            
  $(document).on('buttonClick', function() {
    box.text('Clicked!');
  });
});

.box { background-color: red; }

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

<div class="box">Hi</div>
<button class="clickme">Click me</button>

More info on jQuery Triggers

I would suggest you override the addClass function. You can do it this way:

// Create a closure
(function(){
    // Your base, I'm in it!
    var originalAddClassMethod = jQuery.fn.addClass;

    jQuery.fn.addClass = function(){
        // Execute the original method.
        var result = originalAddClassMethod.apply( this, arguments );

        // call your function
        // this gets called everytime you use the addClass method
        myfunction();

        // return the original result
        return result;
    }
})();

// document ready function
$(function(){
    // do stuff
});

change() does not fire when a CSS class is added or removed or the definition changes. It fires in circumstances like when a select box value is selected or unselected.

I'm not sure if you mean if the CSS class definition is changed (which can be done programmatically but is tedious and not generally recommended) or if a class is added or removed to an element. There is no way to reliably capture this happening in either case.

You could of course create your own event for this but this can only be described as advisory. It won't capture code that isn't yours doing it.

Alternatively you could override/replace the addClass() (etc) methods in jQuery but this won't capture when it's done via vanilla Javascript (although I guess you could replace those methods too).