[Adept Software Development] JavaScript Events - Part 4 - Event Library Source

[Paul Marrington]

As promised, here it is. Refer to the earlier articles if you want to know the hows and whys.

/*
 * Created on 5/11/4
 *
 * Copyright 2004 Paul Marrington
 * All rights reserved - http://marringtons.com
 * PROPRIETARY/CONFIDENTIAL
 * Use is subject to license terms - pa...@marrington.net
 */

/**
 * Add all the events in an event object
 * inside the group given.
 */
Events.addEvents = function( element, group)
  {
    for (var name in group.events)
      Events.add(
        element, name, group.events[name]);
  }

Events.addSameEvent = function(
  name, action, elements)
  {
    for (var i = 2;  i < arguments.length;  i++)
      Events.add( arguments[i], name, action);
  }

Events.add = function( element, name, action)
  {
    name = name.toLowerCase();
    var on = "on" + name;

    if (! element.events)
      element.events = new Object();
    
    var list = element.events[name];
    if (! list)
      {
        list = element.events[name] = new Array();
        if (element[on]) list.push( element[on]);
        /*
         * This is an interesting bit of obscure code.
         * If there were any other way, I would not do
         * it, but IE makes it essential. The event handler
         * is inline so that it keeps a handle to the surrounding
         * function/object. This way we can set event.owner
         * to the same as the calling element when add
         * function was called - even though the event
         * handler is called asynchronously later,
         * long after the add function is dead and buried.
         * Nasty. It also means we are hanging on to an
         * unknown amount of stuff. The W3C DOM uses
         * evt.currentTarget, but this is the ONLY way
         * we can get IE to know the owner. This is
         * because evt.target is the actual element
         * clicked on or whatever, while the owner 
         * of the event can be further up the DOM tree.
         */
        element[on] = function( evt)
          {
            /*
             * Normalise the event object between
             & browsers and retrieve the list
             * of actions to take.
             */
            evt = evt || event;
            if (! evt.target)
              evt.target = evt.srcElement;
            /*
             * We get element from the owner object.
             */
            evt.owner = element;

            var list = this.events[evt.type];
            /*
             * Run each event in the list until
             * one returns false. This breaks the chain.
             * Events are run from the most
             * recently added to the oldest.
             */
            for (var i = list.length - 1;  i >= 0;  i--)
              {
                evt.action = list[i];
                if (! evt.action( evt))
                  return false;
              }
            return true;
          }
      }
    
    list.push( action);
  }

Events.newList = function( name)
  {
    var newList = function( evt)
      {
        for (var j = evt.action.events.length - 1; 
          j >= 0;  j--)
            if (! evt.action.events[j]( evt))
              return false;
        return true;
      }
    newList.eventName = name;
    newList.events = new Array();
    newList.add = function( event)
      {
        this.events.push( event);
      }
    return newList;
  }

 

--
Posted by Paul Marrington to Adept Software Development at 9/20/2005 06:28:00 PM