CCNumberAuthenticator/Q2_imtiaz3.html at master · Zayan19/CCNumberAuthenticator · GitHub

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<!DOCTYPE html>
<html>
<body>

First Name: <input type="text" id="myText" value="">

<p>Please enter a Visa, Master Card or American Express credit card number.</p>

<button onclick="isValidCreditCard()">Try it</button>

<p id="demo"></p>

<script>
function isValidCreditCard() {
    var inputText = document.getElementById("myText").value;
    var total= 0 + parseInt (inputText[inputText.length-1]);
    var alt = 1;

//if the structure is valid set this variable to 1
    var checkValidStructure = 2;
//check valdity of credit card length and numbers using regular expressions:

    if ( inputText.match(/^5[12345].{14}/)!=null||
            inputText.match(/^3[47].{13}/)!=null||
            inputText.match(/^4[1-9].{11}/)!=null||
            inputText.match(/^4[1-9].{14}/)!=null)
    {

        checkValidStructure = 1;
    }


//remove the last element
    var cNum = inputText.slice(0,-1);
    var b = 0;
//Luhn's algorithm implementation
//multiplies every other digit by two starting from the right most
//if double digits add the two digits
//add up all the digits

    for (var i = cNum.length-1; i >= 0; i--) {
        if (alt==1) {
            b= parseInt(cNum[i])*2;

            if (b.toString().length>1) {
            var a = parseInt(cNum[i])*2;
            var n = parseInt(a.toString()[0])+parseInt(a.toString()[1]);
            total=total+n;
            }

            else {
                total = total+b;
            }
            alt=0;
    }
        else {
            total = total+parseInt(cNum[i]);
            alt=1;
        }

    }

//check if the sum + the last digit is a multiple of 10 as well
    //to confirm checksum digit
//confirm if  the structure was valid or not
    if (total%10==0&& checkValidStructure==1) {
        document.getElementById("demo").innerHTML = "valid";
        checkValidStructure = 0;
    }
    else {
        document.getElementById("demo").innerHTML = "invalid";
    }
}

</script>
</body>
</html>
</script></p>
</body>
</html>