Refactoring permalink checker to handle multiple requests elegantly

app/assets/javascripts/admin/enterprises/controllers/permalink_controller.js.coffee

@@ -1,17 +1,23 @@
 angular.module("admin.enterprises")
   .controller "permalinkCtrl", ($scope, PermalinkChecker) ->
-    $scope.pristinePermalink = $scope.Enterprise.permalink
+    # locals
+    initialPermalink = $scope.Enterprise.permalink
+    pendingRequest = null
+
+    # variables on $scope
     $scope.availablility = ""
     $scope.checking = false
 
     $scope.$watch "Enterprise.permalink", (newValue, oldValue) ->
-      if newValue == $scope.pristinePermalink
-        $scope.availability = ""
-      else
-        $scope.checking = true
-        PermalinkChecker.check(newValue).then (data) ->
-          $scope.availability = 'Available'
-          $scope.checking = false
-        , (data) ->
-          $scope.availability = 'Unavailable'
-          $scope.checking = false
+      $scope.checking = true
+      pendingRequest = PermalinkChecker.check(newValue)
+
+      pendingRequest.then (data) ->
+        if data.permalink == initialPermalink
+          $scope.availability = ""
+        else
+          $scope.availability = data.available
+        $scope.Enterprise.permalink = data.permalink
+        $scope.checking = false
+      , (data) ->
+        # Do nothing (this is hopefully an aborted request)

app/assets/javascripts/admin/enterprises/services/permalink_checker.js.coffee

@@ -1,11 +1,36 @@
 angular.module("admin.enterprises").factory 'PermalinkChecker', ($q, $http) ->
   new class PermalinkChecker
-    check: (permalink) ->
-      deferred = $q.defer()
-      $http.get("/enterprises/check_permalink?permalink=#{permalink}", { headers: { 'Accept': 'application/javascript' } } )
-      .success( (data) ->
-        deferred.resolve data
-      ).error (data) ->
-        deferred.reject(data)
+    deferredRequest: null
+    deferredAbort: null
 
-      deferred.promise
+    check: (permalink) =>
+      @abort(@deferredAbort) if @deferredRequest && @deferredRequest.promise
+      @deferredRequest = deferredRequest = $q.defer()
+      @deferredAbort = deferredAbort = $q.defer()
+      request = $http(
+        method:   "GET"
+        url:      "/enterprises/check_permalink?permalink=#{permalink}"
+        headers:
+          Accept: 'application/javascript'
+        timeout: deferredAbort.promise
+      )
+      .success( (data) =>
+        deferredRequest.resolve
+          permalink: data
+          available: "Available"
+      ).error (data,status) =>
+        if status == 409
+          deferredRequest.resolve
+            permalink: data
+            available: "Unavailable"
+        else
+          # Something went wrong or request was aborted
+          deferredRequest.reject()
+
+      deferredRequest.promise.finally ->
+        request = deferredRequest.promise = null;
+
+      deferredRequest.promise
+
+    abort: (deferredAbort) ->
+      deferredAbort.resolve()