JAvaScript認証コード

function get_code(code_length){ //     
    var rand_aa="";  //     
    var code=new Array("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","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");  //              
    var code_Num=code.length;  //     
    for(i=0;i<code_length;i++){  //     ，     
        //Math.random()              
        //parseInt     ，               
        var ran_ss=parseInt(Math.random()*code_Num);
        rand_aa+=String(code[ran_ss]); //          
    }
    document.write("<input type=text name=check_code size="+code_length+" value="+rand_aa+" class=blank_bg maxsize=10 readonly=true>");//       
}