javascript创建含数字字母的随机字符串

//code from http://caibaojian.com/js-random-string.html
function makeid()
{
  var text = "";
  var possible = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
 
  for( var i=0; i < 5; i++ )
    text += possible.charAt(Math.floor(Math.random() * possible.length));
 
  return text;
}

function randomstring(L){
  var s= '';
  var randomchar=function(){
   var n= Math.floor(Math.random()*62);
   if(n<10) return n; //1-10
   if(n<36) return String.fromCharCode(n+55); //A-Z
   return String.fromCharCode(n+61); //a-z
  }
  while(s.length< L) s+= randomchar();
  return s;
}
   
alert(randomstring(5))

function randomString(len, charSet) {
  charSet = charSet || 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
  var randomString = '';
  for (var i = 0; i < len; i++) {
   var randomPoz = Math.floor(Math.random() * charSet.length);
   randomString += charSet.substring(randomPoz,randomPoz+1);
  }
  return randomString;
}

var randomValue = randomString(5);
 
var randomValue = randomString(5, 'PICKCHARSFROMTHISSET');