PLEASE HELP!! I cant figure out how to have chosen credit card type to have prefix numers at start validated with javascript

Question

if (document.orderform.CreditCardNumber.value.length < 16) { //Checking the card number is 16 digits

alert("Sorry, You need to enter Your Credit Card Number. It must be 16 digits!")

return false

}

              for (var i=0;i<document.orderform.CreditCardNumber.value.length;i++){

temp=document.orderform.CreditCardNumber.value.substring(i,i+1)

if (digits.indexOf(temp)==-1){

alert("Invalid Credit Card Number, Only use Numbers, It must be 16 digits!")

return false

}

}

Answer 1

Try this function

function checkNum(numString) {
var re= new RegExp(/^\d{16}$/);
if(!numString.match(re)) {
console.log("16 numbers are required");
return false
}
console.log("16 numbers entered");
return true;

}

checkNum(document.orderForm.creditCardNumber.value);