原生js做的手风琴效果的导航菜单

var heads = document.querySelectorAll(".first-level");
function headClick(event){
var target = EventUtil.getTarget(event);
toggleDisplay(target.parentNode.querySelector("ul"));
}
for(var i=0;iEventUtil.addHandler(heads[i], "click", headClick);
}

window.Onunload= function (){
for(var i=0;iEventUtil.removeHandler(heads[i], "click", headClick);
}
heads = null;
}

var EventUtil = {
addHandler : function (element, type, handler) {
if (element.addEventListener) {
element.addEventListener(type, handler, false);
} else if (element.attachEvent) {
element.attachEvent("on" + type, handler);
} else {
element["on" + type] = handler;
}
},
removeHandler : function (element, type, handler) {
if (element.removeEventListener) {
element.removeEventListener(type, handler, false);
} else if (element.detachEvent) {
element.detachEvent("on" + type, handler);
} else {
element["on" + type] = null;
}
},
getEvent : function (event) {
return event || window.event;
},
getTarget : function (event) {
return event.target || event.srcElement;
}
}


var getStyle = function (el, style) {
if (el.currentStyle) {
style = style.replace(/\-(\w)/g, function (all, letter) {
return letter.toUpperCase();
});
var value = el.currentStyle[style];
return value;
} else {
return document.defaultView.getComputedStyle(el, null).getPropertyValue(style);
}
}


var toggleDisplay = function (element) {
var display = getStyle(element, "display");
if (display == "none") {
element.style.display = "block";
} else {
element.style.display = "none";
}
}