Implement Array.observe and emit splice change records for ArrayPush

src/object-observe.js

Index: src/object-observe.js
diff --git a/src/object-observe.js b/src/object-observe.js
index c4c6c14a3ada5c740bdd19623bc3f949dabf359b..d82370f20d2f01c0ac16d1a013d126cd75fd7311 100644
--- a/src/object-observe.js
+++ b/src/object-observe.js
@@ -166,7 +166,7 @@ function EndPerformChange(objectInfo, type) {
                        objectInfo);
 }
 
-function ensureObserverRemoved(objectInfo, callback) {
+function EnsureObserverRemoved(objectInfo, callback) {
   function remove(observerList) {
     for (var i = 0; i < observerList.length; i++) {
       if (observerList[i].callback === callback) {
@@ -219,7 +219,7 @@ function ObjectObserve(object, callback, accept) {
   if (IS_UNDEFINED(objectInfo)) objectInfo = CreateObjectInfo(object);
   %SetIsObserved(object, true);
 
-  ensureObserverRemoved(objectInfo, callback);
+  EnsureObserverRemoved(objectInfo, callback);
 
   var observer = CreateObserver(callback, accept);
   if (ObserverIsActive(observer, objectInfo))
@@ -240,7 +240,7 @@ function ObjectUnobserve(object, callback) {
   if (IS_UNDEFINED(objectInfo))
     return object;
 
-  ensureObserverRemoved(objectInfo, callback);
+  EnsureObserverRemoved(objectInfo, callback);
 
   if (objectInfo.changeObservers.length === 0 &&
       objectInfo.inactiveObservers.length === 0) {
@@ -250,6 +250,17 @@ function ObjectUnobserve(object, callback) {
   return object;
 }
 
+function ArrayObserve(object, callback) {
+  return ObjectObserve(object, callback, ['new',
+                                          'updated',
+                                          'deleted',
+                                          'splice']);
+}
+
+function ArrayUnobserve(object, callback) {
+  return ObjectUnobserve(object, callback);
+}
+
 function EnqueueChangeRecord(changeRecord, observers) {
   // TODO(rossberg): adjust once there is a story for symbols vs proxies.
   if (IS_SYMBOL(changeRecord.name)) return;
@@ -271,6 +282,38 @@ function EnqueueChangeRecord(changeRecord, observers) {
   }
 }
 
+function BeginPerformSplice(array) {
+  var objectInfo = objectInfoMap.get(array);
+  if (!IS_UNDEFINED(objectInfo))
+    BeginPerformChange(objectInfo, 'splice');
+}
+
+function EndPerformSplice(array) {
+  var objectInfo = objectInfoMap.get(array);
+  if (!IS_UNDEFINED(objectInfo))
+    EndPerformChange(objectInfo, 'splice');
+}
+
+function EnqueueSpliceRecord(array, index, removed, deleteCount, addedCount) {
+  var objectInfo = objectInfoMap.get(array);
+  if (IS_UNDEFINED(objectInfo) || objectInfo.changeObservers.length === 0)
+    return;
+
+  var changeRecord = {
+    type: 'splice',
+    object: array,
+    index: index,
+    removed: removed,

[adamk, 2013/05/16 00:45:30]

Spec question: are we OK with the 'removed' array being mutable? It seems a bit
off to freeze the changeRecord but not the array. Of course, even after I speed
up freeze, frozen arrays will still be slow, so...

[rafaelw, 2013/05/16 01:10:48]

I think the answer is probably yes. Arv?

The freezing isn't for security, it's for observers not messing with each other,
(and so we don't need to create one for each observer).

I've added a todo (all freezing is disabled right now). The bummer is that even
with Adamk's work on freezing, frozen array's are likely to be slow, but I think
Adam & Toon have some ideas about this for the future, so maybe there's hope.

On 2013/05/16 00:45:30, adamk wrote:

+    addedCount: addedCount
+  };
+
+  changeRecord.removed.length = deleteCount;
+  // TODO(rafaelw): This breaks spec-compliance. Re-enable when freezing isn't
+  // slow.
+  // ObjectFreeze(changeRecord);
+  EnqueueChangeRecord(changeRecord, objectInfo.changeObservers);
+}
+
 function NotifyChange(type, object, name, oldValue) {
   var objectInfo = objectInfoMap.get(object);
   if (objectInfo.changeObservers.length === 0)
@@ -405,6 +448,10 @@ function SetupObjectObserve() {
     "observe", ObjectObserve,
     "unobserve", ObjectUnobserve
   ));
+  InstallFunctions($Array, DONT_ENUM, $Array(
+    "observe", ArrayObserve,
+    "unobserve", ArrayUnobserve
+  ));
   InstallFunctions(notifierPrototype, DONT_ENUM, $Array(
     "notify", ObjectNotifierNotify,
     "performChange", ObjectNotifierPerformChange