js产生几位随机文件名

var chars = ['0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'];
function generateMixed(an) {
var res = "";
for(var ia = 0; ia < an ; ia ++) {
var id = Math.ceil(Math.random()*35);
res += chars[id];
}
return res;
}