From e16016b8b5adb1bf1f2a5ee4677a043ec0a562c4 Mon Sep 17 00:00:00 2001
From: Matthew Grove <matthew@grove.gq>
Date: Wed, 14 Nov 2018 19:07:01 +0000
Subject: [PATCH] Check input isn't null before evaluating the number

---
 luhn-algorithm/script.js | 29 +++++++++++++++++------------
 1 file changed, 17 insertions(+), 12 deletions(-)

diff --git a/luhn-algorithm/script.js b/luhn-algorithm/script.js
index b4434da..7745fec 100644
--- a/luhn-algorithm/script.js
+++ b/luhn-algorithm/script.js
@@ -12,18 +12,23 @@ document.addEventListener("keyup", function(event) {
 
 // function for validating number entered with Luhn algorithm
 function checkNumber() {
-    // retrieve digits & reverse
-    var digits = document.getElementsByTagName("input")[0].value.split("").reverse(), sum = 0;
-    digits.forEach(function(currentDigit, index) {
-        newDigit = Number(currentDigit);
-        if (index % 2 == 1) {
-            if ((newDigit *= 2) > 9) {
-                newDigit -= 9;
+    // define input string and remove non-numerical characters
+    var input = document.getElementsByTagName("input")[0].value.replace(/\D/g,'');;
+    // check string isn't empty
+    if (input) {
+        // retrieve digits & reverse
+        var digits = document.getElementsByTagName("input")[0].value.split("").reverse(), sum = 0;
+        digits.forEach(function(currentDigit, index) {
+            newDigit = Number(currentDigit);
+            if (index % 2 == 1) {
+                if ((newDigit *= 2) > 9) {
+                    newDigit -= 9;
+                }
             }
-        }
-        sum += newDigit;
-    });
+            sum += newDigit;
+        });
 
-    // displays evaluation message
-    $("#validation_message").html(((sum % 10) == 0) ? "Number is valid" : "Number is invalid");
+        // displays evaluation message
+        $("#validation_message").html(((sum % 10) == 0) ? "Number is valid" : "Number is invalid");
+    }
 }