_.barrier + tests

underscore.js

@@ -510,6 +510,14 @@
     };
   };
 
+  // Returns a function that will only be executed after being called N times.
+  _.barrier = function(func, times) {
+    return function() {
+      if (--times === 0) { return func.apply(this, arguments); }
+    };
+  };
+
+
   // Object Functions
   // ----------------