JS: Luhn: Add solution

1 files changed, 34 insertions, 0 deletions

diff --git a/javascript/luhn/luhn.js b/javascript/luhn/luhn.js
new file mode 100644
index 0000000..166a0bf
--- /dev/null
+++ b/javascript/luhn/luhn.js
@@ -0,0 +1,34 @@
+'use strict';
+
+export const valid = (input) => {
+    let filtered = [];
+
+    // Filter the numbers out. Return false if we find anything other
+    // than numbers or spaces.
+    for (let idx = 0; idx < input.length; idx++) {
+        if (/^\d$/.test(input[idx]))
+            filtered.push(Number(input[idx]));
+        else if (!(/^\s$/.test(input[idx])))
+            return false;
+    }
+
+    // Invalid.
+    if (filtered.length < 2)
+        return false;
+
+    // Reverse the filtered numbers.
+    filtered.reverse();
+
+    let sum = 0;
+    for (let idx = 0; idx < filtered.length; idx++) {
+        if ((idx % 2) !== 0) {
+            if ((filtered[idx] * 2) > 9)
+                sum += (filtered[idx] * 2) - 9;
+            else
+                sum += filtered[idx] * 2;
+        } else
+            sum += filtered[idx];
+    }
+
+    return (sum % 10 === 0);
+};