主动驱动事件执行--createEvent

1. createEvent（eventType）
参数：eventType 共5种类型：
    Events ：包括所有的事件. 
          HTMLEvents：包括 'abort', 'blur', 'change', 'error', 'focus', 'load', 'reset', 'resize', 'scroll', 'select', 
                                    'submit', 'unload'. 事件
          UIEvents ：包括 'DOMActivate', 'DOMFocusIn', 'DOMFocusOut', 'keydown', 'keypress', 'keyup'.
                                  间接包含 MouseEvents. 
          MouseEvents：包括 'click', 'mousedown', 'mousemove', 'mouseout', 'mouseover', 'mouseup'. 
          MutationEvents:包括 'DOMAttrModified', 'DOMNodeInserted', 'DOMNodeRemoved', 
                                      'DOMCharacterDataModified', 'DOMNodeInsertedIntoDocument', 
                                      'DOMNodeRemovedFromDocument', 'DOMSubtreeModified'. 

2. 在createEvent后必须初始化，为大家介绍5种对应的初始化方法
  HTMLEvents 和 通用 Events：
            initEvent( 'type', bubbles, cancelable )
    UIEvents ：
                      initUIEvent( 'type', bubbles, cancelable, windowObject, detail )
    MouseEvents： 
                      initMouseEvent( 'type', bubbles, cancelable, windowObject, detail, screenX, screenY, 
                      clientX, clientY, ctrlKey, altKey, shiftKey, metaKey, button, relatedTarget )
    MutationEvents ：
                      initMutationEvent( 'type', bubbles, cancelable, relatedNode, prevValue, newValue, 
                      attrName, attrChange ) 

3. 在初始化完成后就可以随时触发需要的事件了，为大家介绍targetObj.dispatchEvent(event)
    使targetObj对象的event事件触发
  需要注意的是在IE 5.5+版本上请用fireEvent方法，还是浏览兼容的考虑

4. 例子
    //例子1  立即触发鼠标被按下事件
    var fireOnThis = document.getElementByIdx_x('someID');
        var evObj = document.createEvent('MouseEvents');
        evObj.initMouseEvent( 'click', true, true, window, 1, 12, 345, 7, 220, false, false, true, false, 0, null );
        fireOnThis.dispatchEvent(evObj);

  //例子2  考虑兼容性的一个鼠标移动事件
    var fireOnThis = document.getElementByIdx_x('someID');
    if( document.createEvent ) 
    {
        var evObj = document.createEvent('MouseEvents');
        evObj.initEvent( 'mousemove', true, false );
        fireOnThis.dispatchEvent(evObj);
    }
  else if( document.createEventObject )
  {
      fireOnThis.fireEvent('onmousemove');
  }