JSFiddle - React, Tailwind, and code Playground

HTML

<h3>  Sample test number to use -- copy and paste should work </p=h3>
<p>487013675311199070109160101300</p>

<input id="searchTxt" placeholder="add numbers together">
<div id='numberValue'>Number goes here</div>

JavaScript

window.onkeyup = keyup;
        var number;

        function keyup(e) {
            number = e.target.value;
            $('#numberValue').text(number);
            // must be 10 characters long
            if (number.length !== 30) {
                return false;
            }
            number = "" + (number || "");
            // run the checksum
            var valid = false;
            try {
                var sum = (parseInt(number[0]) * 7) +
                        (parseInt(number[1]) * 3) +
                        (parseInt(number[2])) +
                        (parseInt(number[3]) * 7) +
                        (parseInt(number[4]) * 3) +
                        (parseInt(number[5])) +
                        (parseInt(number[6]) * 7) +
                        (parseInt(number[7]) * 3) +
                        (parseInt(number[8]));
                alert(((sum % 10).toFixed(0)));
                var checkDigit = ((sum % 10).toFixed(0));

                if ((number[9]) === ("" + checkDigit)) {
                    alert('Our Checkdigit is valid', checkDigit);
                    valid = true;
                }
            } catch (e) {
                alert('Fail for check 1!');
                valid = false;
            }
            try {
                var sum2 = (parseInt(number[13]) * 7) +
                        (parseInt(number[14]) * 3) +
                        (parseInt(number[15])) +
                        (parseInt(number[16]) * 7) +
                        (parseInt(number[17]) * 3) +
                        (parseInt(number[18]));
                alert(((sum2 % 10).toFixed(0)));
                var checkDigit2 = ((sum2 % 10).toFixed(0));

                if ((number[19]) === ("" + checkDigit2)) {
                    alert('Our Checkdigit2 is valid', checkDigit2);
                    valid = true;
                }
            } catch (e) {
                alert('Fail for check 2!');
                valid = false;
            }
      ...