I am writing a GWT app that will be usable by multiple customers. I'd like
for my customers to be able to customize the app, both on the server side
and client side by writing JavaScript. In other words, they could do things
like:
- Set some configuration for their site, like its name, their web site URL,
address, items on their site, etc.
- Write a JavaScript function to, for example, calculate the price for some
item based on its properties. So the price calculation could be done on
both the client and server, and no recompiling would be needed to change
the price calculation.
The beauty of this is that they could write the JavaScript, and it could be
run using JSNI on the client and Rhino on the server, giving consistent
results. This could also get me out of the business of writing a bunch of
administrative UI code to handle the many possibilities for customization
that customers would want, and also give them much more flexibility,
particularly for price calculations, where the customers want endless
flexibility, and writing a rules engine to handle all of those cases would
be very complicated.
Obviously, the JavaScript they write has to be runnable on both the client
and server. And, if it's just a matter of returning primitives or the
customer writing functions that take and return primitives, it's easy.
Simple JavaScript code snippets like this:
var myname='Joe';
function getMyName() { return 'Joe' };
can be syntactically the same for both JSNI and Rhino.
But the fun soon ends. Let's say I want to allow them to call into methods
in Java classes that I've defined, so I can give them an API to do useful
things. The syntax for accessing Java objects from JavaScript is vastly
different between Rhino and JSNI:
// Rhino
com.abc.package.MyClass.getSomethingUseful();
// JSNI: first in Java
public static native String exportGetSomethingUseful() /*-{
getSomethingUseful =
$entry(@com.abc.package.MyClass::getSomethingUseful());
}-*/;
// JSNI: then in JavaScript
getSomethingUseful();
The situation gets more challenging if you want to pass instances of your
own Java classes into JavaScript for their use, or call from JavaScript
into APIs defined in Java. You've got to define host objects in Rhino, and
I'm not even sure how you do it in JSNI without writing glue code by hand
so that they wouldn't have to learn JSNI's arcane syntax,
My question is: I don't think it's possible for the JavaScript syntax to be
the same between JSNI and Rhino without writing some glue code on both the
client and server in JavaScript to insulate them from these syntactical
differences when working with APIs defined in Java. Am I right, or have I
missed anything?
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