Ensure a window context always exists

We always care about window resizes to refresh trigger points,
but previously if a developer only had non-window-context waypoints
the window resize handler would never exist and no auto resize
refreshes would happen. This commit ensures there is always
a window context so there is always a window resize handler.

Author: imakewebthings

src/context.js

@@ -30,6 +30,10 @@
     element.waypointContextKey = this.key
     contexts[element.waypointContextKey] = this
     keyCounter += 1
+    if (!Waypoint.windowContext) {
+      Waypoint.windowContext = true
+      Waypoint.windowContext = new Context(window)
+    }
 
     this.createThrottledScrollHandler()
     this.createThrottledResizeHandler()
@@ -46,7 +50,8 @@
   Context.prototype.checkEmpty = function() {
     var horizontalEmpty = this.Adapter.isEmptyObject(this.waypoints.horizontal)
     var verticalEmpty = this.Adapter.isEmptyObject(this.waypoints.vertical)
-    if (horizontalEmpty && verticalEmpty) {
+    var isWindow = this.element == this.element.window
+    if (horizontalEmpty && verticalEmpty && !isWindow) {
       this.adapter.off('.waypoints')
       delete contexts[this.key]
     }
@@ -292,6 +297,7 @@
     Context.refreshAll()
   }
 
+
   Waypoint.requestAnimationFrame = function(callback) {
     var requestFn = window.requestAnimationFrame ||
       window.mozRequestAnimationFrame ||

test/context-spec.js

@@ -71,12 +71,6 @@ window.jQuery.each(Waypoint.adapters, function(i, adapter) {
           $scroller.scrollTop($target.offset().top)
           expect(currentDirection).toBeNull()
         })
-
-        it('removes context from global lookup', function() {
-          skipDestroy = true
-          context.destroy()
-          expect(Waypoint.Context.findByElement(window)).toBeFalsy()
-        })
       })
 
       describe('Waypoint.Context.refreshAll()', function() {