Created
January 28, 2014 19:31
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| <html> | |
| <head> | |
| <script> | |
| function check_cc() { | |
| var r = document.getElementById("results"); | |
| var elem = document.getElementById("ccnum"); | |
| r.innerHTML = "Checking CC: " + elem.value + "<br>"; | |
| var result = valid_credit_card(elem.value); | |
| r.innerHTML = r.innerHTML + "Valid? " + result + "<br>"; | |
| } | |
| // takes the form field value and returns true on valid number | |
| function valid_credit_card(value) { | |
| // accept only digits, dashes or spaces | |
| if (/[^0-9-\s]+/.test(value)) return "Invalid format"; | |
| // The Luhn Algorithm. It's so pretty. | |
| var nCheck = 0, nDigit = 0, bEven = false; | |
| value = value.replace(/\D/g, ""); | |
| for (var n = value.length - 1; n >= 0; n--) { | |
| var cDigit = value.charAt(n), | |
| nDigit = parseInt(cDigit, 10); | |
| if (bEven) { | |
| if ((nDigit *= 2) > 9) nDigit -= 9; | |
| } | |
| nCheck += nDigit; | |
| bEven = !bEven; | |
| } | |
| return (nCheck % 10) == 0; | |
| } | |
| </script> | |
| </head> | |
| <body> | |
| <p>Enter your credit card number:</p> | |
| <input id="ccnum" type="text"></input> | |
| <button onclick="check_cc();">Check</button> | |
| <h3>Results</h3> | |
| <p id="results"></p> | |
| </body> | |
| </html> |
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