Fixes #465 -- throttled functions return their value when they actually run.

test/functions.js

@@ -117,12 +117,15 @@ $(document).ready(function() {
     _.delay(function(){ equal(value, 6, "updated to latest value"); start(); }, 400);
   });
 
-  asyncTest("functions: throttle once", 1, function() {
+  asyncTest("functions: throttle once", 2, function() {
     var counter = 0;
-    var incr = function(){ counter++; };
+    var incr = function(){ return ++counter; };
     var throttledIncr = _.throttle(incr, 100);
-    throttledIncr();
-    _.delay(function(){ equal(counter, 1, "incr was called once"); start(); }, 220);
+    var result = throttledIncr();
+    _.delay(function(){
+      equal(result, 1, "throttled functions return their value");
+      equal(counter, 1, "incr was called once"); start();
+    }, 220);
   });
 
   asyncTest("functions: throttle twice", 1, function() {

underscore.js

@@ -531,7 +531,7 @@
   // 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, more;
+    var context, args, timeout, throttling, more, result;
     var whenDone = _.debounce(function(){ more = throttling = false; }, wait);
     return function() {
       context = this; args = arguments;
@@ -544,10 +544,11 @@
       if (throttling) {
         more = true;
       } else {
-        func.apply(context, args);
+        result = func.apply(context, args);
       }
       whenDone();
       throttling = true;
+      return result;
     };
   };