Modular Haxe JS

This project demonstrates the creation of a Haxe-JavaScript modular project with on-demand loading of modules (JS + CSS).

It's really easy and absolutely transparent in the code!

How it works

Haxe compiler can exclude classes or entire packages

Compiler argument to exclude one class

--macro exclude('module1.Module1')

Compiler argument to exclude an entire package:

--macro exclude('module1')

You should simply create several JS files with the code you want, excluding the code to share.

The trick to join several JS modules

Haxe JS can expose a class to the global context:

package module1;

@:expose
class Module1 {
}

The Haxe compiler will make the class available globally (normally window or exports) and, if the class was excluded, expect that it is available already globally.

The only problem is that it's not really clean to have every shared attached to window, but with a tiny change to Haxe JS output, it is possible to transparently "merge" the scopes of the different loaded JS files, so that the main JS can instantiate classes from modules, and so that modules can extend classes from the main JS or some other module.

The first part of the "hack" is really as simple as that:

// replace in JS output
$hx_exports.com = $hx_exports.com || {};
// by
var com = $hx_exports.com = $hx_exports.com || {};

Secondly, we don't want to expose on the global scope so we're changing Haxe default to a "private" shared scope called $hx_scope.

On-demand loading

These combined allows us to:

• build modules as separate JS files
• build main application with modules excluded,
• load modules at runtime.

Example

Building:

The hxml script defines common build properties, then builds the module and then the main application. Obviously you can create several build scripts instead.

Here's the example script explained:

1. Common compiler options

   Those should include the Stub.modules() macro which does the JS modification previously described, and finishing by --each to start defining builds.

    -cp src
    -debug
    --macro util.Stub.modules()
    --each
   

2. The builds (the order doesn't matter)

   The important part is to use the --exclude macro to ommit classes/packages that are expected to be loaded, and --next between each module. Here we only have -main for the main JS because we want the static main to be executed.

    -js bin/module1.js
    module1.Module1
    --macro exclude('com.common')
   
    --next
   
    -js bin/index.js
    -main Main
    --macro exclude('module1')
   

Loading

This sample project includes a utility class to load modules at run time, as well as its associated CSS file if desired.

The function Require.module(name, loadCss) returns a promise.

Require.module('module1').then(moduleLoaded, moduleFailed);

function moduleLoaded(name) {
	new Module1(); // that's all
}

If loading any resource fails, the promise will be rejected and you'll be able to call the method again to retry loading the module.

Gotchas

• Shared classes can not be in the global package.

• In a module, you MUST @:expose every type that you will explicitly use in your main application's code (new, Std.is, Type reflection...).

• Also if you are going to use reflection in the main application (eg. Std.is), you MUST use some reflection in the modules code, otherwise the compiler will not generate the reflection metadata. Alternatively you can set -dce no in the compiler arguments for the module.

• The utility class uses the browser ES6 Promise object - make sure to include a shim if you want to target a wide range of browsers.

• There's no clean way to actually expose something to window or exports; you can do it explicitly for now (a little macro could solve it I guess):

    untyped window.MyPublicClass = MyPublicClass
    untyped exports.MyPublicClass = MyPublicClass
  

Further improvements

The provided utility classes seems to be working nicely in modern browsers but it wasn't tested on a real project - we'll probably discover subtle issues...

What about some React hot-reload? It should be possible :)