js實現一個簡單的自定義右鍵菜單

var RightMenu = function(){
        this.rightMenu = null;
        this.rightMenuList = [];
        this.itemIndex = 0;
    }
    RightMenu.prototype = {
        init:function(){
            this._preventDefaultRightMenu(); //初始化時阻止默認事件
            this._createRightMenu();         //創建右鍵菜單
            this._rightClickEvent();         // 添加點擊右鍵菜單的事件
        },
        _preventDefaultRightMenu:function(){
            document.addEventListener('contextmenu',function(event){ 
                event.preventDefault();
            },false)            
        },
        _createRightMenu:function(){
            this.rightMenu = document.createElement('ul');
            this.rightMenu.id = 'rightMenu';
            document.body.appendChild(this.rightMenu);
        },
        _rightClickEvent:function(){
            //給document綁定右鍵事件
            document.addEventListener('contextmenu',function(event){
                var menu = document.getElementById('rightMenu');
                menu.style.left = event.clientX + 'px';
                menu.style.top = event.clientY + 'px';
                menu.style.display = 'block';
            },false)            
        },
        _createRightMenuItem:function(item,callback){
            var li = document.createElement('li');
            li.id = 'rightMenuItem_' + this.itemIndex;
            li.innerHTML = item;
            this.rightMenu.appendChild(li);
            li.addEventListener('click',callback,false);
            this.itemIndex++;
        },
        addRightMenuItem:function(itemText,callback){ //供外部調用的方法傳入兩個參數（菜單文字，點擊時的回調函數）
            this.rightMenuList.push(itemText);
            this._createRightMenuItem(itemText,callback);           
        }
    }
    //使用時初始化對象
    var rightMenu = new RightMenu();
    rightMenu.init();
    //添加右鍵菜單和回調函數
    rightMenu.addRightMenuItem('全選',function(event){
        alert('全選')
    });
    rightMenu.addRightMenuItem('單選',function(event){
        alert('單選')
    });