//str_0 长度 
//str_1 是否大写字母 
//str_2 是否小写字母 
//str_3 是否数字 
function rnd_str(str_0,str_1,str_2,str_3) 
{ 
var Seed_array=new Array(); 
var seedary; 
var i; 

Seed_array[0]="" 
Seed_array[1]= "A B C D E F G H J K L M N P Q R S T U V W X Y";
Seed_array[2]= "a b c d e f g h j k l m n p q r s t u v w x y";
Seed_array[3]= "0 1 2 3 4 5 6 7 8 9";


if (!str_1&&!str_2&&!str_3){str_1=true;str_2=true;str_3=true;} 

if (str_1){Seed_array[0]+=Seed_array[1];} 
if (str_2){Seed_array[0]+=" "+Seed_array[2];} 
if (str_3){Seed_array[0]+=" "+Seed_array[3];} 

Seed_array[0]= Seed_array[0].split(" "); 
seedary="" 
for (i=0;i<str_0;i++) 
{ 
seedary+=Seed_array[0][Math.round(Math.random( )*(Seed_array[0].length-1))] 
} 
return(seedary); 

}