このページ内どこでも左クリックでContextMenuが表示されます

以下はこのページのJavaScript

var click = function(type, args){
    var list = args[1];
    if(list){
        document.body.style[list.value.style] = list.value.color;
        for(var i=0, item; item=this.getItem(i); i++){
            item.cfg.setProperty("checked", false);
        }
        this.getItem(list.index).cfg.setProperty("checked", true);
    }
};
var keydown = function(event){
    if(event.shiftKey){
        switch(event.keyCode){
            case 'R'.charCodeAt(0):
                document.body.style.color="red";
            break;
            case 'B'.charCodeAt(0):
                document.body.style.color="blue";
            break;
            case 'Y'.charCodeAt(0):
                document.body.style.color="yellow";
            break;

            case 'G'.charCodeAt(0):
                document.body.style.backgroundColor="gray";
            break;
            case 'W'.charCodeAt(0):
                document.body.style.backgroundColor="white";
            break;
        }
    }
};
var backgroundcolors = [
    {text:"灰", value:{style:"backgroundColor", color:"gray"}, helptext:"Shift + G"},
    {text:"白", value:{style:"backgroundColor", color:"white"}, helptext:"Shift + W"}
];
var fontcolors = [
    {text:"赤", value:{style:"color", color:"red"}, helptext:"Shift + R"},
    {text:"青", value:{style:"color", color:"blue"}, helptext:"Shift + B"},
    {text:"黄", value:{style:"color", color:"yellow"}, helptext:"Shift + Y"}
];

var init = function(){
    var ctxmenu = new YAHOO.widget.ContextMenu('ctxmenu', {
        trigger: document,
        itemdata: [
            {text:"背景", submenu:{id:"ctxmenu1", itemdata: backgroundcolors}},
            {text:"フォント", submenu:{id:"ctxmenu2", itemdata: fontcolors}}
        ]
    });
    ctxmenu.render(document.body);

    var menubar = new YAHOO.widget.MenuBar('menubar', {
        itemdata: [
            {text:"背景", submenu:{id:"menubar1", itemdata: backgroundcolors}},
            {text:"フォント", submenu:{id:"menubar2", itemdata: fontcolors}}
        ]
    });
    menubar.render("top");

    for(var i=0, item; item=ctxmenu.getItem(i); i++){
        item.cfg.getProperty('submenu').clickEvent.subscribe(click);
    }
    for(var i=0, item; item=menubar.getItem(i); i++){
        item.cfg.getProperty('submenu').clickEvent.subscribe(click);
    }

    YAHOO.util.Event.addListener(document.body, 'keydown', keydown);
};

YAHOO.util.Event.addListener(window, 'load', init);