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');