Merge pull request #486 from jamestalmage/fix-debounce-timing-corner-case

Fix: utils.debounce timing corner case.

Author: katowulf

src/utils.js

@@ -62,6 +62,7 @@
             var queue = [];
             var start;
             var cancelTimer;
+            var runScheduledForNextTick;
 
             // returns `fn` wrapped in a function that queues up each call event to be
             // invoked later inside fo runNow()
@@ -77,14 +78,17 @@
             }
 
             // clears the current wait timer and creates a new one
-            // however, if maxWait is exceeded, calls runNow() immediately
+            // however, if maxWait is exceeded, calls runNow() on the next tick.
             function resetTimer() {
               if( cancelTimer ) {
                 cancelTimer();
                 cancelTimer = null;
               }
               if( start && Date.now() - start > maxWait ) {
-                utils.compile(runNow);
+                if(!runScheduledForNextTick){
+                  runScheduledForNextTick = true;
+                  utils.compile(runNow);
+                }
               }
               else {
                 if( !start ) { start = Date.now(); }
@@ -96,6 +100,7 @@
             function runNow() {
               cancelTimer = null;
               start = null;
+              runScheduledForNextTick = false;
               var copyList = queue.slice(0);
               queue = [];
               angular.forEach(copyList, function(parts) {
@@ -114,7 +119,7 @@
            * @param {int} [maxWait] max milliseconds to wait before sending out, defaults to wait * 10 or 100
            */
           debounce: function(fn, ctx, wait, maxWait) {
-            var start, cancelTimer, args;
+            var start, cancelTimer, args, runScheduledForNextTick;
             if( typeof(ctx) === 'number' ) {
               maxWait = wait;
               wait = ctx;
@@ -130,25 +135,29 @@
             if( !maxWait ) { maxWait = wait*10 || 100; }
 
             // clears the current wait timer and creates a new one
-            // however, if maxWait is exceeded, calls runNow() immediately
+            // however, if maxWait is exceeded, calls runNow() on the next tick.
             function resetTimer() {
               if( cancelTimer ) {
                 cancelTimer();
                 cancelTimer = null;
               }
               if( start && Date.now() - start > maxWait ) {
-                utils.compile(runNow);
+                if(!runScheduledForNextTick){
+                  runScheduledForNextTick = true;
+                  utils.compile(runNow);
+                }
               }
               else {
                 if( !start ) { start = Date.now(); }
                 cancelTimer = utils.wait(runNow, wait);
               }
             }
 
-            // Clears the queue and invokes all of the functions awaiting notification
+            // Clears the queue and invokes the debounced function with the most recent arguments
             function runNow() {
               cancelTimer = null;
               start = null;
+              runScheduledForNextTick = false;
               fn.apply(ctx, args);
             }
 

tests/unit/utils.spec.js

@@ -51,6 +51,42 @@ describe('$firebaseUtils', function () {
     });
   });
 
+  describe('#debounce', function(){
+    it('should trigger function with arguments',function(){
+      var spy = jasmine.createSpy();
+      $utils.debounce(spy,10)('foo', 'bar');
+      $timeout.flush();
+      expect(spy).toHaveBeenCalledWith('foo', 'bar');
+    });
+
+    it('should only trigger once, with most recent arguments',function(){
+      var spy = jasmine.createSpy();
+      var fn =  $utils.debounce(spy,10);
+      fn('foo', 'bar');
+      fn('baz', 'biz');
+      $timeout.flush();
+      expect(spy.calls.count()).toBe(1);
+      expect(spy).toHaveBeenCalledWith('baz', 'biz');
+    });
+
+    it('should only trigger once (timing corner case)',function(){
+      var spy = jasmine.createSpy();
+      var fn =  $utils.debounce(spy, null, 1, 2);
+      fn('foo', 'bar');
+      var start = Date.now();
+
+      // block for 3ms without releasing
+      while(Date.now() - start < 3){ }
+
+      fn('bar', 'baz');
+      fn('baz', 'biz');
+      expect(spy).not.toHaveBeenCalled();
+      $timeout.flush();
+      expect(spy.calls.count()).toBe(1);
+      expect(spy).toHaveBeenCalledWith('baz', 'biz');
+    });
+  });
+
   describe('#updateRec', function() {
     it('should return true if changes applied', function() {
       var rec = {};