Filter plugin no longer tries to navigate annotations if there are none

src/plugin/filter.coffee

@@ -287,26 +287,39 @@ class Annotator.Plugin.Filter extends Annotator.Plugin
     filter = $(event.target).parent().data('filter')
     this.updateFilter filter if filter
 
-  # Locates the next highlighted element in @highlights from the current one
-  # or goes to the very first element.
+  # Locates the next/previous highlighted element in @highlights from the
+  # current one or goes to the very first/last element respectively.
   #
-  # event - A click Event.
+  # previous - If true finds the previously highlighted element.
   #
-  # Returns nothing
-  _onNextClick: (event) =>
+  # Returns itself.
+  _findNextHighlight: (previous) ->
+    return this unless @highlights.length
+
+    offset      = if previous then 0    else -1
+    resetOffset = if previous then -1   else 0
+    operator    = if previous then 'lt' else 'gt'
+
     active  = @highlights.not('.' + @classes.hl.hide)
     current = active.filter('.' + @classes.hl.active)
-    unless current.length
-      current = active.eq(-1)
+    current = active.eq(offset) unless current.length
 
-    annotation = current.data('annotation')
+    annotation = current.data 'annotation'
 
-    index = active.index(current[0])
-    next  = active.filter(':gt(' + index + ')').not(annotation.highlights).eq(0)
-    unless next.length
-      next = active.eq(0)
+    index = active.index current[0]
+    next  = active.filter(":#{operator}(#{index})").not(annotation.highlights).eq(resetOffset)
+    next  = active.eq(resetOffset) unless next.length
 
-    this._scrollToHighlight(next.data('annotation').highlights)
+    this._scrollToHighlight next.data('annotation').highlights
+
+  # Locates the next highlighted element in @highlights from the current one
+  # or goes to the very first element.
+  #
+  # event - A click Event.
+  #
+  # Returns nothing
+  _onNextClick: (event) =>
+    this._findNextHighlight()
 
   # Locates the previous highlighted element in @highlights from the current one
   # or goes to the very last element.
@@ -315,18 +328,7 @@ class Annotator.Plugin.Filter extends Annotator.Plugin
   #
   # Returns nothing
   _onPreviousClick: (event) =>
-    active  = @highlights.not('.' + @classes.hl.hide)
-    current = active.filter('.' + @classes.hl.active)
-    unless current.length
-      current = active.eq(0)
-    annotation = current.data('annotation')
-
-    index = active.index(current[0])
-    prev  = active.filter(':lt(' + index + ')').not(annotation.highlights).eq(-1)
-    unless prev.length
-      prev = active.eq(-1)
-
-    this._scrollToHighlight(prev.data('annotation').highlights)
+    this._findNextHighlight true
 
   # Scrolls to the highlight provided. An adds an active class to it.
   #

test/spec/plugin/filter_spec.coffee

@@ -324,6 +324,11 @@ describe "Filter", ->
           plugin._onNextClick()
           expect(plugin._scrollToHighlight).toHaveBeenCalledWith([element3[0]])
 
+        it "should do nothing if there are no annotations", ->
+          plugin.highlights = $()
+          plugin._onNextClick()
+          expect(plugin._scrollToHighlight).not.toHaveBeenCalled()
+
       describe "_onPreviousClick", ->
         it "should advance to the previous element", ->
           element3.addClass(plugin.classes.hl.active)
@@ -342,9 +347,14 @@ describe "Filter", ->
         it "should only navigate through non hidden elements", ->
           element3.addClass(plugin.classes.hl.active)
           element2.addClass(plugin.classes.hl.hide)
-          plugin._onNextClick()
+          plugin._onPreviousClick()
           expect(plugin._scrollToHighlight).toHaveBeenCalledWith([element1[0]])
 
+        it "should do nothing if there are no annotations", ->
+          plugin.highlights = $()
+          plugin._onPreviousClick()
+          expect(plugin._scrollToHighlight).not.toHaveBeenCalled()
+
     describe "_scrollToHighlight", ->
       mockjQuery = null