https://okouchi.co.jp/data/common/c1001a017301/js/dropdown.js

1var menu=function(){
2	var t=15,z=50,s=6,a;
3	function dd(n){this.n=n; this.h=[]; this.c=[]}
4	dd.prototype.init=function(p,c){
5		a=c; var w=document.getElementById(p), s=w.getElementsByTagName('ul'), l=s.length, i=0;
6		for(i;i<l;i++){
7			var h=s[i].parentNode; this.h[i]=h; this.c[i]=s[i];
8			h.onmouseover=new Function(this.n+'.st('+i+',true)');
9			h.onmouseout=new Function(this.n+'.st('+i+')');
10		}
11	}
12	dd.prototype.st=function(x,f){
13		var c=this.c[x], h=this.h[x], p=h.getElementsByTagName('a')[0];
14		clearInterval(c.t); c.style.overflow='hidden';
15		if(f){
16			p.className+=' '+a;
17			if(!c.mh){c.style.display='block'; c.style.height=''; c.mh=c.offsetHeight; c.style.height=0}
18			if(c.mh==c.offsetHeight){c.style.overflow='visible'}
19			else{c.style.zIndex=z; z++; c.t=setInterval(function(){sl(c,1)},t)}
20		}else{p.className=p.className.replace(a,''); c.t=setInterval(function(){sl(c,-1)},t)}
21	}
22	function sl(c,f){
23		var h=c.offsetHeight;
24		if((h<=0&&f!=1)||(h>=c.mh&&f==1)){
25			if(f==1){c.style.filter=''; c.style.opacity=1; c.style.overflow='visible'}
26			clearInterval(c.t); return
27		}

28		var d=(f==1)?Math.ceil((c.mh-h)/s):Math.ceil(h/s), o=h/c.mh;
29		c.style.opacity=o; c.style.filter='alpha(opacity='+(o*100)+')';
30		c.style.height=h+(d*f)+'px'
31	}
32	return{dd:dd}
33}();