[ ▼ 질문관련 참고 Source ]

//cookie.js
function getCookieVal (offset) {
   var endstr = document.cookie.indexOf (";", offset);
   if (endstr == -1) endstr = document.cookie.length;
   return unescape(document.cookie.substring(offset, endstr));
}
function GetCookie (name) {
   var arg = name + "=";
   var alen = arg.length;
   var clen = document.cookie.length;
   var i = 0;
   while (i < clen) { //while open
      var j = i + alen;
      if (document.cookie.substring(i, j) == arg)
         return getCookieVal (j);
      i = document.cookie.indexOf(" ", i) + 1;
      if (i == 0) break; 
   } //while close
   return null;
}
function SetCookie (name, value) {
   var argv = SetCookie.arguments;
   var argc = SetCookie.arguments.length;
   var expires = (2 < argc) ? argv[2] : null;
   var path = (3 < argc) ? argv[3] : null;
   var domain = (4 < argc) ? argv[4] : null;
   var secure = (5 < argc) ? argv[5] : false;
   document.cookie = name + "=" + escape (value) +
      ((expires == null) ? "" : 
         ("; expires=" + expires.toGMTString())) +
      ((path == null) ? "" : ("; path=" + path)) +
      ((domain == null) ? "" : ("; domain=" + domain)) +
      ((secure == true) ? "; secure" : "");
}

function checkCookie(name)        //쿠키의 존재 유무를 알아내는 함수를 만듭니다.
{
        var nameOfCookie = name + "=";
        var x = 0;
        while(x <= document.cookie.length)
        {
                var y = (x + nameOfCookie.length);
                if(document.cookie.substring(x,y) == nameOfCookie)
                {
                        if((endOfCookie = document.cookie.indexOf(";",y)) == -1)
                                endOfCookie = document.cookie.length;
                        return unescape(document.cookie.substring(y,endOfCookie));
                }
                x = document.cookie.indexOf(" ",x) + 1;
                if(x == 0)
                        break;
        }
        return "";
}

function DelCookie(cKey) {   
    var date = new Date();  
    var validity = -1;
    date.setDate(date.getDate() + validity);
    document.cookie =
          cKey + "=;expires=" + date.toGMTString();
}

//sidebar
if (checkCookie("sidebar_oc") != "ok" )     
{
	SetCookie('sidebar_oc', 0);
	var checkSidebar = GetCookie("sidebar_oc");
} else {
	var checkSidebar = GetCookie("sidebar_oc");
}

var side_content = function() { 
var __sidecontent = document.getElementById('sidecontent'); 
var __sidebtn = document.getElementById('_sidebtn'); 

if (checkSidebar=1)
	{
		__sidecontent.style.display = "block"; 
		__sidebtn.src="<?=$g4[path]?>/img/btn_side_close.png";
	} else if (checkSidebar=0)
	{
		__sidecontent.style.display = "none"; 
		__sidebtn.src="<?=$g4[path]?>/img/btn_side_open.png";
	}

function sideOnOff(checkSidebar) {
	if (checkSidebar=1)
	{
		DelCookie('sidebar_oc');
		SetCookie('sidebar_oc', 0);
		side_content();
	} else if (checkSidebar=0)
	{
		DelCookie('sidebar_oc');
		SetCookie('sidebar_oc', 1);
		side_content();
	}

//onoff button
<a href="javascript:sideOnOff(checkSidebar);">