Client Express - Require and Exports

I recently introduced you to Client Express where I explained that the goal is to copy the API of Express (Node.js) but for use on the client. This will enable you to share code between the server and the client, specifically the routing.

And I got a pretty decent part done when I blogged about it, but that was one major difference and that was that on the server you use require to include different JavaScript libraries and within these libraries you would use exports to export your functionality to the application.

require(‘…’)

Below here you see two common uses of require, the first one require(‘express’) is to add the Express module and the second one require(__dirname + ‘/examples/server_routing’ ).example_routing() is to load a local JavaScript file and execute the function example_routing() which is defined inside this JavaScript file.

exports….

Here we see the local JavaScript file that was loaded using require in the above example. Important to note here is that we see how exports is used to expose the function example_routing() to the user of the library.

And now in the browser

Well both require and exports do not exist in the browser, so we need to add them. There are already different approaches that enable you to use require I believe all of them are an implementation of CommonJS so I added my own implementation for that to Client Express and after some tuning and a pull request I got that to work nicely.

The thing I didn’t see was how people solved the exports problem. And because I didn’t want to stop halfway I started thinking and came up with the following solution. My require will try to download the requested JavaScript file if it cannot find the module in the registered modules. When it is downloaded it will then do something EVIL it will do the following:

That’s right I am using eval to evaluate the JavaScript text found in the downloaded JavaScript file and attach the exported functions to my exports object. After the eval my exports object is then placed in the registered modules so this process only happens once. After that the exports object is returned from the require function exposing the functions defined in the just downloaded JavaScript file.

This enables me to use the exact same syntax on the server as on the client for both require and exports. See below here the full implementation:

Now as you can see I am always defining these functions even if an other library has defined them already, but I do copy the registered modules from those other libraries.

One problem is when my CommonJS implementation is overwritten by some library loaded after my Client Express because then I would loose the download and eval capabilities. So for the time being my library needs to either be loaded last, or the other libraries should check for existence of the require functionality and if it exists don’t overwrite it.

I am however thinking about a way that overwrites it again after the Client Express server has started ensuring it will work when during runtime the code requires additional libraries.

Please let me know what you think.