How can I share code between Node.js and the browser?
I am creating a small application with a JavaScript client (run in the browser) and a Node.js server, communicating using WebSocket.
I would like to share code between the client and the server. I have only just started with Node.js and my knowledge of modern JavaScript is a little rusty, to say the least. So I am still getting my head around the CommonJS require() function. If I am creating my packages by using the 'export' object, then I cannot see how I could use the same JavaScript files in the browser.
I want to create a set of methods and classes that are used on both ends to facilitate encoding and decoding messages, and other mirrored tasks. However, the Node.js/CommonJS packaging systems seems to preclude me from creating JavaScript files that can be used on both sides.
I also tried using JS.Class to get a tighter OO model, but I gave up because I couldn't figure out how to get the provided JavaScript files to work with require(). Is there something am I missing here?
If you want to write a module that can be used both client side and server side, I have a short blog post on a quick and easy method: Writing for Node.js and the browser, essentially the following (where this is the same as window ):
(function(exports){
// Your code goes here
exports.test = function(){
return 'hello world'
};
})(typeof exports === 'undefined'? this['mymodule']={}: exports);
Alternatively there are some projects aiming to implement the Node.js API on the client side, such as Marak's gemini.
You might also be interested in DNode, which lets you expose a JavaScript function so that it can be called from another machine using a simple JSON-based network protocol.
Epeli has a nice solution here http://epeli.github.com/piler/ that even works without the library, just put this in a file called share.js
(function(exports){
exports.test = function(){
return 'This is a function from shared module';
};
}(typeof exports === 'undefined' ? this.share = {} : exports));
On the server side just use:
var share = require('./share.js');
share.test();
And on the client side just load the js file and then use
share.test();
Don't forget that the string representation of a JavaScript function represents the source code for that function. You could simply write your functions and constructors in an encapsulated way so they can be toString()'d and sent to the client.
Another way to do it is use a build system, put the common code in separate files, and then include them in both the server and client scripts. I'm using that approach for a simple client/server game via WebSockets where the server and client both run essentially the same game loop and the client synchronises up with the server every tick to make sure nobody's cheating.
My build system for the game is a simple Bash script that runs the files through the C preprocessor and then through sed to clean up some junk cpp leaves behind, so I can use all the normal preprocessor stuff like #include, #define, #ifdef, etc.
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