指定した名前のcookieを取得

引用元: ポンパレ

function get_cookie(name){
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 "";
}