JQuery右键菜单插件contextmenu事件控制右键事件

window.onload = function(e) {
    var showimgtag = document.getElementById('showimgtag'),
        showimgtagF = showimgtag.parentNode,
        menu = document.getElementById('menu');
   
    addHandler(showimgtag, 'contextmenu', function(e){
        e = e || window.event;
        preventDefault(e);
       
        menu.style.left = e.pageX+'px';
        menu.style.top = e.pageY+'px';
        menu.style.display = 'block';
        menu.innerHTML = '© '+'author';
    });
 
    addHandler(menu, 'contextmenu', function(e){
        e = e || window.event;
        preventDefault(e);
    });
 
    addHandler(document, 'mousedown', function(e){
        e = e || window.event;
        var obj = e.srcElement?e.srcElement:e.target;
        if(isChild(menu, obj)){
            return false;
        }
        menu.style.display = 'none';
    });
};
 
function isChild(parent, child) {
    while (child != null) {
        if (child == parent) {
            return true;
        }
        child = child.parentNode;
    }
    return false;
}
 
function addHandler(element, type, handler) {
    if(element.addEventListener){
        element.addEventListener(type,handler,false);
    }else{
        element.attachEvent('on'+type,handler);
    }
}
 
function preventDefault(e){
    e = e || window.event;
    if(e.preventDefault){
        e.preventDefault();
    }else{
        e.returnValue = false;
    }
}