chore(debounce): create debounce helper

- Create internal debounce helper
- Move debounce logic from typeahead to use helper

Closes #3966
Closes #4813

src/debounce/debounce.js

@@ -0,0 +1,21 @@
+angular.module('ui.bootstrap.debounce', [])
+/**
+ * A helper, internal service that debounces a function
+ */
+  .factory('$$debounce', ['$timeout', function($timeout) {
+    return function(callback, debounceTime) {
+      var timeoutPromise;
+
+      return function() {
+        var self = this;
+        var args = Array.prototype.slice(arguments);
+        if (timeoutPromise) {
+          $timeout.cancel(timeoutPromise);
+        }
+
+        timeoutPromise = $timeout(function() {
+          callback.apply(self, args);
+        }, debounceTime);
+      };
+    };
+  }]);

src/debounce/test/debounce.spec.js

@@ -0,0 +1,40 @@
+describe('$$debounce', function() {
+  var $$debounce, $timeout, debouncedFunction, i;
+
+  beforeEach(module('ui.bootstrap.debounce'));
+  beforeEach(inject(function(_$$debounce_, _$timeout_) {
+    $$debounce = _$$debounce_;
+    $timeout = _$timeout_;
+    i = 0;
+    debouncedFunction = $$debounce(function() {
+      i++;
+    }, 100);
+  }));
+
+  it('should function like a $timeout when called once during timeout', function() {
+    debouncedFunction();
+    $timeout.flush(50);
+
+    expect(i).toBe(0);
+
+    $timeout.flush(50);
+
+    expect(i).toBe(1);
+  });
+
+  it('should only execute 100ms after last call when called twice', function() {
+    debouncedFunction();
+    $timeout.flush(50);
+
+    expect(i).toBe(0);
+
+    debouncedFunction();
+    $timeout.flush(50);
+
+    expect(i).toBe(0);
+
+    $timeout.flush(50);
+
+    expect(i).toBe(1);
+  });
+});

src/typeahead/typeahead.js

@@ -1,4 +1,4 @@
-angular.module('ui.bootstrap.typeahead', ['ui.bootstrap.position'])
+angular.module('ui.bootstrap.typeahead', ['ui.bootstrap.debounce', 'ui.bootstrap.position'])
 
 /**
  * A helper service that can parse typeahead's syntax (string provided by users)
@@ -26,8 +26,8 @@ angular.module('ui.bootstrap.typeahead', ['ui.bootstrap.position'])
     };
   }])
 
-  .controller('UibTypeaheadController', ['$scope', '$element', '$attrs', '$compile', '$parse', '$q', '$timeout', '$document', '$window', '$rootScope', '$uibPosition', 'uibTypeaheadParser',
-    function(originalScope, element, attrs, $compile, $parse, $q, $timeout, $document, $window, $rootScope, $position, typeaheadParser) {
+  .controller('UibTypeaheadController', ['$scope', '$element', '$attrs', '$compile', '$parse', '$q', '$timeout', '$document', '$window', '$rootScope', '$$debounce', '$uibPosition', 'uibTypeaheadParser',
+    function(originalScope, element, attrs, $compile, $parse, $q, $timeout, $document, $window, $rootScope, $$debounce, $position, typeaheadParser) {
     var HOT_KEYS = [9, 13, 27, 38, 40];
     var eventDebounceTime = 200;
     var modelCtrl, ngModelOptions;
@@ -264,8 +264,16 @@ angular.module('ui.bootstrap.typeahead', ['ui.bootstrap.position'])
       $document.find('body').bind('scroll', fireRecalculating);
     }
 
-    // Declare the timeout promise var outside the function scope so that stacked calls can be cancelled later
-    var timeoutEventPromise;
+    // Declare the debounced function outside recalculating for
+    // proper debouncing
+    var debouncedRecalculate = $$debounce(function() {
+      // if popup is visible
+      if (scope.matches.length) {
+        recalculatePosition();
+      }
+
+      scope.moveInProgress = false;
+    }, eventDebounceTime);
 
     // Default progress type
     scope.moveInProgress = false;
@@ -276,20 +284,7 @@ angular.module('ui.bootstrap.typeahead', ['ui.bootstrap.position'])
         scope.$digest();
       }
 
-      // Cancel previous timeout
-      if (timeoutEventPromise) {
-        $timeout.cancel(timeoutEventPromise);
-      }
-
-      // Debounced executing recalculate after events fired
-      timeoutEventPromise = $timeout(function() {
-        // if popup is visible
-        if (scope.matches.length) {
-          recalculatePosition();
-        }
-
-        scope.moveInProgress = false;
-      }, eventDebounceTime);
+      debouncedRecalculate();
     }
 
     // recalculate actual position and set new values to scope