coderofsalvation · November 16, 2016 13:41 · Nov 16, 2016
diff --git a/spy.js b/spy.js
@@ -0,0 +1,16 @@
+function spy (fn) {
+  if (!fn) fn = function() {};
+
+  function proxy() {
+    var args = Array.prototype.slice.call(arguments);
+    proxy.calls.push(args);
+    proxy.called = true;
+    fn.apply(this, args);
+  }
+
+  proxy.prototype = fn.prototype;
+  proxy.calls = [];
+  proxy.called = false;
+
+  return proxy;
+}