[Clug-tech] JavaScript objects and inheritance

[John Jardine]

Thanks for the pointer to JSON.  I'm going to pursue two approaches: 1)
Directly access Java objects from JavaScript & ActionScript and (2)
passing them back and forth with JSON.  This may well come down to which
approach (works/is easier) for my partner.

On Wed, 2008-09-03 at 12:49 -0600, Shawn wrote:
> Sounds to me like you are looking for JSON.
> 
> JSON is just a string representation of an object.
> 
> So, using your generic Java Message you might send the following string:
> 
> { "msg_version": "value1", "msg_userid": "value2", "msg_session": "value3", "msg_class": "value4", "msg_type": "value5" }
> 
> This "object" would be the myMessage object.  Of course that can be extended 
> as needed.  You can pass arrays, objects, or even methods this way.  That 
> string is simple javascript so can be converted back to an object 
> quickly/easily.  There are safe and unsafe ways of doing this, at one extreme 
> is just using an eval statement
> 
> var myMessage = eval(json_string);
> 
> This isn't considered "safe" as it can easily introduce script injection 
> issues.  But it does work fine, and is suitable if the json_string is from a 
> trusted source.  There are other/safer methods - a little googling for JSON 
> will lead you to them.  (don't know them off the top of my head - I usually 
> just use the jQuery library for this)
> 
> So, for your specific problem, you might have something on the client side 
> that looks like this:
> 
> function dataArrives(data_string) {
>   var myMessage = eval(dataString);
>   switch (myMessage.msg_type) {
>     case "login":  doLogin(myMessage.login_name, myMessage.password); break;
>     //etc.
>   }
> }
> 
> As for "extending" the core object when needed, that is a simple case of 
> setting or adding other properties when needed.  In JS there is nothing 
> special needed here.
> 
> var myMessage = standardMessageObject;
> myMessage.johnsName = "John";
> 
> Converting your object to string can also be done via code:
> 
> function toJson(target) {
>   var out = "{";
>   for (p in target) {
>     out += "\"" + p + "\": \"" + target[p] + "\", ";
>   }
>   out += "}";
>   return out;
> }
> 
> There are more robust functions available for this on the web.  That is just 
> off the top of my head.
> 
> This is totally client side.  Most server side languages have a method for 
> converting an existing object to a JSON string, and/or creating an object 
> from a JSON string.  And because it is simple string manipulation, processing 
> overhead is very minimal - depending on the complexity/volume of your data.
> 
> Oh, Actionscript is just a variant of ECMAScript (aka JavaScript).  So all 
> this should work just fine in flash, or in the browser.
> 
> here's some links to help get you started.
> 
> http://www.json.org/
> http://www.google.ca/search?q=json&ie=utf-8&oe=utf-8&aq=t&rls=com.ubuntu:en-US:unofficial&client=firefox-a
> 
> HTH  (and hope I haven't completely missed your need here..)
> 
> Shawn
> 
> 
> On Wednesday 03 September 2008 11:12:36 John Jardine wrote:
> > I was wondering if there is an easy way to this...
> > I am sending messages between a server and a flash file running in a
> > browser.
> >
> > The browser is using a Java applet to send/receive the data because it's
> > UDP based.  The messages all start out the same (header info) but differ
> > 16 bytes in, based on the type of data they'll carry. I'd like to be
> > able to do it via a somewhat generic object.
> >
> > So to summarize the current data flow:
> > Internet UDP packets <=> Java <=> JavaScript <=> ActionScript
> >
> > In a perfect world I'd like to have ActionScript send/rcv UDP
> > packets ... but it's not a perfect world.  This has led me to the
> > current method.  Now I'm trying to make the client message handling more
> > generic and a little less fragile.
> >
> > What I'd like to end up with is a generic Java message:
> > public class myMessage {
> > public int msg_version;
> > public int msg_userid;
> > public int msg_session;
> > public int msg_class;
> > public int msg_type;
> > .
> > .
> > .
> > Then extend this generic class with more specific message types:
> > public class myLoginMessage extends myMessage {
> > public int msg_version;
> > public int msg_userid;
> > public int msg_session;
> > public int msg_class;
> > public int msg_type;
> > public String login_name;
> > public String password;
> > .
> > .
> > .
> >
> > Then as these message types arrive, I have Java call JavaScript which
> > retrieves the message and passes it on to ActionScript.
> >
> > Is there a way to do this or am I stuck creating different objects for
> > each message type?
> >
> > Any insight's would be welcome.  I already have something working - I
> > just don't like it and am looking for something better.
> >
> > Another thing... the whole communications design is to off-load the
> > server as much as possible.  I don't care how hard or convoluted the
> > client side gets as long as I can keep my server side ridiculously
> > simple (and blazingly fast).
> >
> >
> > _______________________________________________
> > clug-tech mailing list
> > clug-tech at clug.ca
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> 
> 
> 
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