模拟windows平台的上下文菜单效果代码

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function $(id) {
return document.getElementById(id);
};

var EventUnit = {
addHandler: function(element, type, handler) {//添加事件处理程序
if(element.addEventListener) {
element.addEventListener(type, handler, false);
} else if(element.attachEvent) {
element.attachEvent('on' + type, handler);
} else {
element['on' + type] = handler;
};
},
getEvent: function(event) {
return event ? event : window.event;
},
preventDefault: function(event) {//取消事件默认动作
if(event.preventDefault) {
event.preventDefault();
} else {
event.returnValue = false;
};
}
}

EventUnit.addHandler(window, 'load', function() {
var wrap = $('wrap');
var menu = $('menu');
var menuStyle = menu.style.display;
var x = wrap.offsetLeft + wrap.clientWidth, y = wrap.offsetTop + wrap.clientHeight;
var w = 0, h = 0;
var left = 0, top = 0;

EventUnit.addHandler(wrap, 'contextmenu', function(event) {
event = EventUnit.getEvent(event);
EventUnit.preventDefault(event);

menu.style.display = 'block';
w = menu.clientWidth;
h = menu.clientHeight;
left = (x - event.clientX >= w) ? event.clientX - wrap.offsetLeft : event.clientX - wrap.offsetLeft - w;
top = (event.clientY + h <= y) ? event.clientY - wrap.offsetTop : event.clientY - wrap.offsetTop - h;
menu.style.left = left + 'px';
menu.style.top = top + 'px';
});

EventUnit.addHandler(document, 'click', function() {
menu.style.display = menuStyle;
});
});