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This course shows how to communicate between web pages, both within a single domain and across one or more domains, using the HTML5 Messaging API. Author Bill Weinman reviews security and the same origin policy, details cross-origin scripting techniques, and explores examples of cross-document messaging. The course describes how to register and send messages to listeners and handle errors.
Now let's take a look at a more interactive example of cross-origin messaging. This is a little chat app, and while it may not be terribly useful to chat between two windows on a single desktop, it does give us an opportunity to explore some of the subtleties of the messaging interface. So this application works much like the ones that we've seen so far; in fact it uses a lot of the same code. The first thing that it does is it loads up the second window inside a frame, and then the second window inside a frame sends a message back to the first window to tell it that it's loaded.
So you'll see in the first window, which is the outer one, we have this log "this is windowOne" and its host, one.3sn.net. And windowTwo is on two.3sn.net so they are in different origins. And then once windowTwo gets loaded, it sends this message to windowOne that says, "windowTwo is loaded." And the purpose of that is so that windowOne now has a handle to windowTwo's window object or rather, a window proxy object that works just like its window object. You'll also notice that it says info, and the reason for that is that we're actually sending some structured data that categorizes the different types of messages.
And we have two different types of messages: we have info message and we have chat messages. So when I come up here and I type a message, a chat message, you'll see that that message shows up over here without saying info in front of it. And if I send one over here, you see that it comes up over here without it saying info in front of it. And the reason for that is that there are actually two different categories of messages that are being sent, and it's being sent as structured data with JSON.
And the reason we're using JSON is because this application worked just fine with the structured data except on the Internet Explorer. And in order to for it to work on Internet Explorer, we had to use JSON, because Internet Explorer is only sending strings in its data payload. So now that we've seen how the app works, in the next movie we'll take a look at the code and see how it's implemented.
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