diff --git a/counting-duplicates/index.js b/counting-duplicates/index.js
new file mode 100644
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+++ b/counting-duplicates/index.js
@@ -0,0 +1,8 @@
+// https://www.codewars.com/kata/counting-duplicates/javascript
+
+function duplicateCount(text) {
+  const m = text.toLowerCase().match(/[a-z0-9]/g) || [];
+  const cnt = new Map();
+  m.map(c => cnt.set(c, (cnt.get(c) || 0) + 1));
+  return [...cnt].filter(([k,v])=>1<v).length;
+}