#30 Optimization: send 'data-modified' packets only if needed

Author: janodvarko

lib/firequery-actor.js

@@ -357,6 +357,7 @@ var FireQueryActor = ActorClass(
       return;
     }
 
+    // Bail out if the element has already been cached as modified.
     if (this.modifiedElements.has(element)) {
       return;
     }
@@ -368,22 +369,46 @@ var FireQueryActor = ActorClass(
   }),
 
   /**
-   * Send chunk of modified elements.
+   * Send chunk of modified elements after a timeout.
    */
-  sendDataModified: function() {
+  sendDataModified: makeInfallible(function() {
     this.modifiedElementsTimeout = null;
 
+    let walkerActor = this.conn.getActor(this.walkerActorID);
+
+    // WalkerActor.hasNode() method has been introduced in Firefox 43.
+    // See also: https://bugzilla.mozilla.org/show_bug.cgi?id=1195742
+    // TODO: The workaround can be removed when Fx43 is the minimum
+    // requirement FIXME.
+    let hasNode = typeof(walkerActor.hasNode) == "function" ?
+      walkerActor.hasNode.bind(walkerActor) :
+      walkerActor._refMap.has.bind(walkerActor._refMap);
+
+    // This is an important optimization that can filter list of
+    // packets send to the client down to the bare minimum.
+    // Make sure all modifiedElements are still known by the walker,
+    // they could have been removed during the timeout or they haven't
+    // even been imported by the client yet.
+    for (let node of this.modifiedElements) {
+      if (!hasNode(node)) {
+        this.modifiedElements.delete(node);
+      }
+    }
+
+    // Bail out if there is nothing to send.
     if (!this.modifiedElements.size) {
       return;
     }
 
-    let walkerActor = this.conn.getActor(this.walkerActorID);
     let data = walkerActor.attachElements(this.modifiedElements);
 
+    // Clean up the cache with modified elements.
     this.modifiedElements.clear();
 
+    // Send data modified event to the client,
+    // so the UI can be updated.
     Events.emit(this, "data-modified", data);
-  },
+  }),
 
   /**
    * Returns jQuery data for given node.