Fixing _.throttle() to only execute once if called once. #170 comments.

test/functions.js

@@ -118,6 +118,22 @@ $(document).ready(function() {
     _.delay(function(){ ok(value == 7, "updated to latest value"); start(); }, 400);
   });
 
+  asyncTest("functions: throttle once", 1, function() {
+    var counter = 0;
+    var incr = function(){ counter++; };
+    var throttledIncr = _.throttle(incr, 100);
+    throttledIncr();
+    _.delay(function(){ ok(counter == 1, "incr was called once"); start(); }, 220);
+  });
+
+  asyncTest("functions: throttle twice", 1, function() {
+    var counter = 0;
+    var incr = function(){ counter++; };
+    var throttledIncr = _.throttle(incr, 100);
+    throttledIncr(); throttledIncr();
+    _.delay(function(){ ok(counter == 2, "incr was called twice"); start(); }, 220);
+  });
+
   asyncTest("functions: debounce", 1, function() {
     var counter = 0;
     var incr = function(){ counter++; };

underscore.js

@@ -523,17 +523,21 @@
   // Returns a function, that, when invoked, will only be triggered at most once
   // during a given window of time.
   _.throttle = function(func, wait) {
-    var context, args, timeout, throttling;
+    var context, args, timeout, throttling, more;
-    var whenDone = _.debounce(function(){ throttling = false; }, wait);
+    var whenDone = _.debounce(function(){ more = throttling = false; }, wait);
     return function() {
       context = this; args = arguments;
       var later = function() {
         timeout = null;
-        func.apply(context, args);
+        if (more) func.apply(context, args);
         whenDone();
       };
       if (!timeout) timeout = setTimeout(later, wait);
-      if (!throttling) func.apply(context, args);
+      if (throttling) {
+        more = true;
+      } else {
+        func.apply(context, args);
+      }
       whenDone();
       throttling = true;
     };