Properly generate preview for short jQuery objects

Author: janodvarko

lib/firequery-actor.js

@@ -132,14 +132,24 @@ var FireQueryActor = ActorClass(
       return false;
     }
 
+    let length = DevToolsUtils.getProperty(actor.obj, "length");
+    if (typeof length != "number") {
+      return false;
+    }
+
     let preview = grip.preview = {
       kind: "jQuery",
+      length: length,
     };
 
+    if (actor.threadActor._gripDepth > 1) {
+      return true;
+    }
+
+    preview.items = [];
+
     let raw = actor.obj.unsafeDereference();
-    let items = preview.items = [];
-    let length = DevToolsUtils.getProperty(actor.obj, "length");
-    for (let i = 0; i < length; ++i) {
+    for (let i = 0; i < preview.length; ++i) {
       // Array Xrays filter out various possibly-unsafe properties (like
       // functions, and claim that the value is undefined instead. This
       // is generally the right thing for privileged code accessing untrusted
@@ -152,7 +162,7 @@ var FireQueryActor = ActorClass(
         value = makeDebuggeeValueIfNeeded(actor.obj, value);
 
         let grip = actor.threadActor.createValueGrip(value);
-        items.push(grip);
+        preview.items.push(grip);
 
         let cache = hasJQueryCache(desc.value);
         if (cache) {
@@ -163,10 +173,10 @@ var FireQueryActor = ActorClass(
           // xxxHonza: generate preview for the cache?
         }
       } else {
-        items.push(null);
+        preview.items.push(null);
       }
 
-      if (items.length == OBJECT_PREVIEW_MAX_ITEMS) {
+      if (preview.length == OBJECT_PREVIEW_MAX_ITEMS) {
         break;
       }
     }