TL;DR: Keep your C++ class member declaration order the same as your constructor member initializers order.

C++ guarantees that the member initializers in a constructor are called in order. However the order in which they are called is the order in which the associated members are declared in the class, not the order in which they appear in the member initializer list. For instance, take the following code. I would have thought it would print "three, one, two", but in fact it prints, "one, two, three".

   
      #include "stdafx.h"
#include 

class PrintSomething {
public:
 PrintSomething(const wchar_t *name) { std::wcout << name << std::endl; }
};

class NoteOrder {
public:
        // This order doesn't matter.
 NoteOrder() : three(L"three"), one(L"one"), two(L"two") { }

 PrintSomething one;
 PrintSomething two;
 PrintSomething three;
};

int wmain(const int argc, const wchar_t* argv[])
{
 NoteOrder note; // Prints one, two, three, not three, one, two!
 return 0;
}

In IE10 and other new browsers one may create MessageChannel objects that have two MessagePorts each connected (w3c spec calls it entangled) to one another such that postMessage on one port results in the message event firing on the other. You can pass an array of ports as the last parameter to postMessage and they show up in the ports property of the message event arg.

Origin

The postMessage here is like the worker postMessage and unlike the window and iframe postMessage in that it applies no origin checking:

1. No origin postMessage in workers and MessagePorts: postMessage(messageData, ports)
2. Origin postMessage in windows and iframes: postMessage(messageData, targetOrigin, ports)

Unfortunately the origin isn't an optional parameter at the end to make the two postMessages have the same signature.

On the event handler side, the event arg always has an origin property. But in the no origin case it is always the empty string.

Source

There is also a source property on the message event arg which if set is an object that has a postMessage property allowing you to post back to your caller. It is set for the origin case, however, in the no origin case this property is null. This is somewhat reasonable because in the case of MessagePort and Workers there are only two endpoints so you always know the source of a message implicitly. Unlike the origin case in which any iframe or window can be calling postMessage on any other iframe or window and the caller is unknown. So not unreasonable but it would be nice if the source property was always set for consistency.

MessageChannel start

When a MessageChannel is created it has two MessagePorts, but until those ports are started they will queue up any messages they receive. Once started they will dispatch all queued messages. Ports don't have to be started to send messages.

A port may be started in two ways, either by explicitly calling the start method on the port, or by setting the onmessage callback property on the port. However, adding an event listener via addEventListener("message", does not start the port. It works this way in IE and Chrome and the spec states this as well.

The justification is that since you can have only one callback via onmessage that once set you must implicitly be ready to receive messages and its fine to start the port. As opposed to the addEventListener in which case the user agent cannot start implicitly because it doesn't know how many event listeners will be added.  I found Hixie stating this justification in geoloc meeting notes.

Links

W3C Spec

Opera introduction

My third completed Windows Store app is Percent Clock which displays portions of a time span like the time of the day or time until your next birthday, as a percentage. This was a small project I had previously started as a webpage and converted and finished as an HTML JavaScript Windows Store app.

The only somewhat interesting aspect of this app is that its the first app for which I tried charging. I picked the minimum amount for price 1.49 USD as it is a simple app and unsurprisingly it has sold very poorly. I'm considering releasing new instances of the app for specific scenarios:

• Death Clock: viewing your current age with respect to your life expectancy as a percentage.
• New Year Countdown: percentage of the year until New Years.

The Windows Runtime API Windows.Foundation.Collections.PropertySet class​ is a nice string name to object value map that has a changed event that fires when the contents of the map is modified. Be careful with this event because it fires synchronously from the thread on which the PropertySet was modified. If modified from the UI thread, the UI thread will then wait as it synchronously dispatches the changed event to all listeners which could lead to performance issues or especially from the UI thread deadlock. For instance, deadlock if you have two threads both trying to tell each other about changed events for different PropertySets.