Generate a 9 digit password

function psw(){
    var num = "";
    var alpha = "abcdefghijklmnopqrstuvwxyz";
    var num_alpha = alpha.toUpperCase() + alpha + "0123456789";
    for (var i = 0; i < 9; i++){
      num += num_alpha.charAt(Math.floor(Math.random() * num_alpha.length));
    }
    return num;
}