導航欄 jQuery 和 native JS

最近在練習原生JS，因而想把幾個月以前用jQuery寫的一個導航的功能，用原生JS實現一遍。

寫JS不到一年，沒作IE8兼容，求大神輕噴，有寫的很差的，求指教~~

• jQuery：

$(".navigation li").addClass("displayNone");

$(".nav_icon").click(function(){
    open_nav();
    return false;
});

$(window).click(function(){
    close_nav();
});
  
function open_nav(){
    $(".navigation").removeClass("displayNone");
    $(".navigation").css("visibility","hidden");
    $(".navigation li").each(function(i){
        var nav_li = $(this);
        setTimeout(function(){
            nav_li.slideDown("fast"); 
        },100+100*i);
        
    });
    $(".navigation").css("visibility","visible");
}

function close_nav(){
    var li_count = $(".navigation li").length;
    $(".navigation li").each(function(i){
        var nav_li = $(this);
        setTimeout(function(){
            nav_li.slideUp("fast");
        },100*li_count-100*i);
    });
}

• native JS (IE9+):

var Navigation = function(){
    var el = this.el = document.getElementsByClassName("navigation")[0];

    var getCurrentHeight = function(){
        if(window.getComputedStyle){
            return window.getComputedStyle(el,null).height;
        }else if(el.currentStyle){
            return el.currentStyle.height;
        }else{
            return el.offsetHeight;
        }
    };

    var navHeight = parseInt(getCurrentHeight());

    this.openList = function(speed){ //speed爲展開用時
        el.style.visibility = "visible";
        var currentHeight = document.getElementsByClassName("navigation")[0].style.height = 0;
        var openTimer = setInterval(function(){
            currentHeight += navHeight*(10/speed);
            el.style.height = currentHeight + "px";
            if(currentHeight >= navHeight){
                el.style.height = navHeight + "px";
                   clearInterval(openTimer);
            }
        },10);
        navStatus ++;
    };
    this.closeList = function(speed){ //speed爲收起用時
        var currentHeight = parseInt(getCurrentHeight()) ;

        var closeTimer = setInterval(function(){
            currentHeight -= navHeight*(10/speed);
            el.style.height = currentHeight + "px";
            if(currentHeight <= 0){
                el.style.height = "0px";
                clearInterval(closeTimer);
            }
        },10);
        navStatus = 0;
    };
}

var navigation = new Navigation();
var navStatus = 0;

document.getElementsByClassName("nav_icon")[0].onclick = function(e){
    if(navStatus == 0){
        navigation.openList(450);
        window.event ? window.event.cancelBubble = true : e.stopPropagation();
    }else{
        navigation.closeList(450);
    }
}    
window.onclick = function(){
    navigation.closeList(450);
}