JS Mass Luhn Checker/Gen V3 Public SRC

<script>
var valcnt=0;
function luhnCheckDigit(number){
var validChars="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ_";
number = number.toUpperCase().trim();
var sum=0;
for(var i=0;i<number.length;i++){
var ch=number.charAt(number.length-i-1);
if(validChars.indexOf(ch)<0){
alert("Invalid Chars Found!!");
return false;
}
var digit=ch.charCodeAt(0)-48;
var weight;
if(ch%2==0){
weight=(2*digit)-parseInt(digit/5)*9;
}else{
weight=digit;
}
sum+=weight;
}
sum=Math.abs(sum)+10;
var digit=(10 -(sum%10))%10;
return digit;
}
var amm=prompt("Enter Ammount:");
var orig=amm;
while(amm!=0){
amm--;
var inn=Math.floor(Math.random()*9999999999999999);
//var inn=prompt("Enter Any Credit Card #:");
var out=luhnCheckDigit(""+inn);
if(out==0){
valcnt++;
var outs=(inn)+"<br>"+outs;

}else{
//alert(inn);
//alert("Invalid Credit Card #!!","","Invalid Number!!");
}
}
if(outs!=undefined){
var clean=outs.replace("undefined","");
document.write(clean);
}
if(valcnt==1){
alert(valcnt+ " Valid Number Generated From "+orig+" Attempts!!");
}else{
alert(valcnt+ " Valid Numbers Generated From "+orig+" Attempts!!");
}
</script>