fixes #170, fixes #266 ... reimplementing throttle in terms of debounce.

test/functions.js

@@ -90,16 +90,32 @@ $(document).ready(function() {
     _.delay(function(){ ok(deferred, "deferred the function"); start(); }, 50);
   });
 
-  asyncTest("functions: throttle", 1, function() {
+  asyncTest("functions: throttle", 2, function() {
     var counter = 0;
     var incr = function(){ counter++; };
     var throttledIncr = _.throttle(incr, 100);
     throttledIncr(); throttledIncr(); throttledIncr();
+    setTimeout(throttledIncr, 70);
     setTimeout(throttledIncr, 120);
     setTimeout(throttledIncr, 140);
+    setTimeout(throttledIncr, 190);
     setTimeout(throttledIncr, 220);
     setTimeout(throttledIncr, 240);
-    _.delay(function(){ ok(counter == 3, "incr was throttled"); start(); }, 400);
+    _.delay(function(){ ok(counter == 1, "incr was called immediately"); }, 30);
+    _.delay(function(){ ok(counter == 4, "incr was throttled"); start(); }, 400);
+  });
+
+  asyncTest("functions: throttle arguments", 2, function() {
+    var value = 0;
+    var update = function(val){ value = val; };
+    var throttledUpdate = _.throttle(update, 100);
+    throttledUpdate(1); throttledUpdate(2); throttledUpdate(3);
+    setTimeout(function(){ throttledUpdate(4); }, 120);
+    setTimeout(function(){ throttledUpdate(5); }, 140);
+    setTimeout(function(){ throttledUpdate(6); }, 260);
+    setTimeout(function(){ throttledUpdate(7); }, 270);
+    _.delay(function(){ ok(value == 1, "updated to latest value"); }, 40);
+    _.delay(function(){ ok(value == 7, "updated to latest value"); start(); }, 400);
   });
 
   asyncTest("functions: debounce", 1, function() {

underscore.js

@@ -520,8 +520,29 @@
     return _.delay.apply(_, [func, 1].concat(slice.call(arguments, 1)));
   };
 
-  // Internal function used to implement `_.throttle` and `_.debounce`.
-  var limit = function(func, wait, debounce) {
+  // Returns a function, that, when invoked, will only be triggered at most once
+  // during a given window of time.
+  _.throttle = function(func, wait) {
+    var timeout, context, args, throttling, finishThrottle;
+    finishThrottle = _.debounce(function(){ throttling = false; }, wait);
+    return function() {
+      context = this; args = arguments;
+      var throttler = function() {
+        timeout = null;
+        func.apply(context, args);
+        finishThrottle();
+      };
+      if (!timeout) timeout = setTimeout(throttler, wait);
+      if (!throttling) func.apply(context, args);
+      if (finishThrottle) finishThrottle();
+      throttling = true;
+    };
+  };
+
+  // Returns a function, that, as long as it continues to be invoked, will not
+  // be triggered. The function will be called after it stops being called for
+  // N milliseconds.
+  _.debounce = function(func, wait) {
     var timeout;
     return function() {
       var context = this, args = arguments;
@@ -529,24 +550,11 @@
         timeout = null;
         func.apply(context, args);
       };
-      if (debounce) clearTimeout(timeout);
-      if (debounce || !timeout) timeout = setTimeout(throttler, wait);
+      clearTimeout(timeout);
+      timeout = setTimeout(throttler, wait);
     };
   };
 
-  // Returns a function, that, when invoked, will only be triggered at most once
-  // during a given window of time.
-  _.throttle = function(func, wait) {
-    return limit(func, wait, false);
-  };
-
-  // Returns a function, that, as long as it continues to be invoked, will not
-  // be triggered. The function will be called after it stops being called for
-  // N milliseconds.
-  _.debounce = function(func, wait) {
-    return limit(func, wait, true);
-  };
-
   // Returns a function that will be executed at most one time, no matter how
   // often you call it. Useful for lazy initialization.
   _.once = function(func) {