var generateId = function (len, prefix, charSet) {
 if (prefix == undefined || prefix == null) {
   prefix = 'ID-';
 }
 
 charSet = charSet || 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
 var randomString = '';
 for (var i = prefix.length ; i < len; i++) {
   var randomPoz = Math.floor(Math.random() * charSet.length);
   randomString += charSet.substring(randomPoz,randomPoz+1);
 }
 return prefix+randomString;
};