Namespaces events without jQuery

a.js

// once in the headers
defineMetaEvent('Namespace','Click');

// then when you need it
document.body.onNamespaceClick.add(function(e) { /*...*/ });
document.body.onNamespaceClick.clear();

b.js

function defineMetaEvent(namespace,realEvent) {
  var eventName = 'on'+namespace+realEvent;
  var realEventLw = realEvent.toLowerCase();
  Object.defineProperty(Element.prototype, eventName, {get:function() {
    
    //
    // where we store the handlers of the meta event:
    //
    var el = this;
    var handlers = [];
    
    //
    // the interface we expose to the world
    //
    var wrapper = {
      
      //
      // add a new handler
      //
      add: function(f) {
        var newLength = handlers.unshift(f); 
        if(newLength==1) { rebind(); }
      },
      
      //
      // remove an existing handler
      //
      remove: function(f) {
        var index = handlers.indexOf(f); if(index>=0) {
          handlers.splice(index, 1);
          if(handlers.length==0) { unbind(); }
        }
      },
      
      //
      // remove all handlers
      //
      clear: function() {
        handlers.length=0; unbind();
      }
      
    };
    
    //
    // the function we use for addEventListener()
    // it calls the handlers, simply
    //
    var metaHandler = function(e) {
      var v = true;
      for(var i=handlers.length; i--;) {
        try { v = !!handlers[i].call(el,e) && v; }
        catch(ex) { setTimeout(function() { throw ex; },0); }
      }
      return v;
    }
    
    //
    // binding metaHandler to the real event
    //
    var unbind = function() {
      el.removeEventListener(realEventLw, metaHandler);
    }
    var rebind = function() {
      el.addEventListener(realEventLw, metaHandler, false);
    }
    
    //
    // caching the wrapper
    //
    Object.defineProperty(el, eventName, {value:wrapper});
    return wrapper;
    
  }});
}