Initial JS stub implementation of Object.observe. Adds support for .object/.unobserve/.notify/.deli…

src/object-observe.js

Index: src/object-observe.js
diff --git a/src/object-observe.js b/src/object-observe.js
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+// Copyright 2012 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+"use strict";
+
+var observerInfoMap = new $WeakMap;
+var objectInfoMap = new $WeakMap;
+
+$Object.observe = function(object, callback) {
+  if (!IS_SPEC_OBJECT(object))
+    throw MakeTypeError("observe_non_object", ["observe"]);
+  if (!IS_SPEC_FUNCTION(callback))
+    throw MakeTypeError("observe_non_function", ["observe"]);
+  if ($Object.isFrozen(callback))
+    throw MakeTypeError("observe_callback_frozen");

[rossberg, 2012/10/24 09:57:24]

I wonder, is this actually necessary? Why does the proposal require it? It seems
useful to be able to use a frozen function as observer. Would it be a side
channel?

[rafaelw, 2012/10/24 11:18:04]

Sadly, yes. This was necessary to prevent a side-channel.

On 2012/10/24 09:57:24, rossberg wrote:

+
+  var observerInfo = observerInfoMap.get(callback);
+  if (IS_UNDEFINED(observerInfo)) {
+    observerInfo = new $Object();

[rossberg, 2012/10/24 09:57:24]

Nit: {} is clearer and potentially more efficient (same below).

[rafaelw, 2012/10/24 11:18:04]

Done.

+    observerInfo.pendingChangeRecords = null;
+    // TODO: setup observerInfo.priority.
+    observerInfoMap.set(callback, observerInfo);
+  }
+
+  var objectInfo = objectInfoMap.get(object);
+  if (IS_UNDEFINED(objectInfo)) {
+    objectInfo = new $Object();
+    objectInfo.changeObservers = new $Array(callback);

[rossberg, 2012/10/24 09:57:24]

Nit: [callback] instead of invoking Array constructor.

[rafaelw, 2012/10/24 11:18:04]

Done.

+    // TODO: setup objectInfo.notifier
+    objectInfoMap.set(object, objectInfo);
+    return;
+  }
+
+  var changeObservers = objectInfo.changeObservers;
+  if (changeObservers.indexOf(callback) >= 0)

[rossberg, 2012/10/24 09:57:24]

Why not use a Set for this?

[rafaelw, 2012/10/24 11:18:04]

AFAIC, The V8 implementation for Map & Set isn't complete. There's no way yet to
iterate over the keys of either.

On 2012/10/24 09:57:24, rossberg wrote:

[rossberg, 2012/10/24 12:03:13]

Ah, you are right of course. Maybe put in a TODO then.

[rafaelw, 2012/10/24 14:56:05]

Done.

+    return;
+
+  changeObservers.push(callback);
+}
+
+$Object.unobserve = function(object, callback) {
+  if (!IS_SPEC_OBJECT(object))
+    throw MakeTypeError("observe_non_object", ["unobserve"]);
+
+  var objectInfo = objectInfoMap.get(object);
+  if (IS_UNDEFINED(objectInfo))

[rossberg, 2012/10/24 09:57:24]

OT: Is there a reason why the spec does not make this in error?

[rafaelw, 2012/10/24 11:18:04]

You mean: unobserving something that isn't observed? Probably to be consistent
with existing listener patterns (e.g. DOM Event Listeners, which also silently
succeed even if the call had no effect).

On 2012/10/24 09:57:24, rossberg wrote:

+    return;
+
+  var observerInfo = observerInfoMap.get(callback);
+
+  var changeObservers = objectInfo.changeObservers;
+  var index = changeObservers.indexOf(callback);
+  if (index < 0)
+    return;
+
+  changeObservers.splice(index, 1);
+}
+
+function EnqueueChangeRecord(changeRecord, observers) {
+  for (var i = 0; i < observers.length; i++) {
+    var observer = observers[i];
+    var observerInfo = observerInfoMap.get(observer);
+
+    // TODO: "activate" the observer
+
+    var pendingChangeRecords = observerInfo.pendingChangeRecords;
+    if (IS_NULL(pendingChangeRecords)) {
+      pendingChangeRecords = observerInfo.pendingChangeRecords = new $Array(changeRecord);

[rossberg, 2012/10/24 09:57:24]

Line too long.

[rafaelw, 2012/10/24 11:18:04]

Done.

+    } else {
+      pendingChangeRecords.push(changeRecord);
+    }
+  }
+}
+
+$Object.notify = function(object, changeRecord) {
+  // TODO: notifier needs to be [[THIS]]

[rossberg, 2012/10/24 09:57:24]

Check that this is an object.

[rafaelw, 2012/10/24 11:18:04]

I asked Arv about this in the spec. He pointed out that its unnecessary.  E.g.

Number.prototype.type = 'updated';
var foo = 5;
foo.type; // 'updated';

On 2012/10/24 09:57:24, rossberg wrote:

+  if (!IS_STRING(changeRecord['type']))

[rossberg, 2012/10/24 09:57:24]

Preferable: changeRecord.type

[rafaelw, 2012/10/24 11:18:04]

Done.

+    throw MakeTypeError("observe_type_non_string");
+
+  var objectInfo = objectInfoMap.get(object);
+  if (IS_UNDEFINED(objectInfo))
+    return;
+
+  var newRecord = new $Object();

[rossberg, 2012/10/24 09:57:24]

{}

[rafaelw, 2012/10/24 11:18:04]

Done.

+  newRecord['object'] = object; // TODO: Needs to be 'object' retreived from notifier

[rossberg, 2012/10/24 09:57:24]

newRecord.object

[rossberg, 2012/10/24 09:57:24]

Line too long

[rafaelw, 2012/10/24 11:18:04]

Done.

+  for (var prop in changeRecord) {
+    if (prop === 'object')
+      continue;
+    newRecord[prop] = changeRecord[prop];
+  }
+  $Object.freeze(newRecord);
+
+  EnqueueChangeRecord(newRecord, objectInfo.changeObservers);
+}
+
+$Object.deliverChangeRecords = function(callback) {
+  if (!IS_SPEC_FUNCTION(callback))
+    throw MakeTypeError("observe_non_function", ["deliverChangeRecords"]);
+
+  var observerInfo = observerInfoMap.get(callback);
+  if (IS_UNDEFINED(observerInfo))
+    return;
+
+  var pendingChangeRecords = observerInfo.pendingChangeRecords;
+  if (IS_NULL(pendingChangeRecords))
+    return;
+
+  observerInfo.pendingChangeRecords = null;
+
+  callback(pendingChangeRecords);
+  return;
+}