JS绑定事件兼容性写法(addHandler、addEvent)

    function addHandler(element,type,handler){   //绑定事件
        if(element.addEventListener){      // IE9以下不兼容
            element.addEventListener(type,handler,false)
        }else if(element.attachEvent){     //IE独有
            element.attachEvent('on' + type ,handler)
        }else{
            element['on'+type] = handler;    //一个元素只能绑定一个处理程序
        }
    }

    function removeHandler(element,type,handler){   //移除事件
        if(element.removeEventListener){      //addEventListener
            element.removeEventListener(type,handler,false)
        }else if(element.detachEvent){           //attachEvent
            element.detachEvent('on' + type,handler)
        }else{
            element['on' + type ] = null;

        }
    }

    function getEvent (event){
        return event ? event : window.event;
    }
    function getTarget(event){  
        return event.target || event.srcElement
    }
    function preventDefault (event){
        if(event.preventDefault){
            event.preventDefault()
        } else{
            event.returnValue = false;
        }
    }
    function stoppropagation(event){
        if(event.stopPropagation){
            event.stopPropagation()
        }else{
            evenvt.cancelBubble = true;
        }
    }