Node-Mod-Load

Lazy load modules and create consistent meta-modules

Working with a huge project means maintaining lots of moduls. Sometimes those modules form circular dependencies, which are not bad by default, but bring lots of problems with them (namely code which will not be executed). In order to solve this problem, modules should be lazy-loaded, meaning they are only required when they are really needed in code; or alternatively modules should not be included at the top of a script but rather at the beginning of the program and then cached. That way even circular dependencies between modules will not be a problem as all code in a module can be read entirely. This module will not solve circular calls. It will only allow circular dependencies and is no excuse for bad programming style and developer's errors!

In addition to regular modules, "meta-modules" can be added and used like every other module in the list of modules. Meta-modules are virtual modules, which are created during runtime. They do not have a separate file for them and should just be a JS-Object which can be used like a module.

This module was first created for SHPS, but then separated for easy use by everyone :)

Installation

Requires Node.JS >= 4

$ npm i node-mod-load

Interface

module.exports = class {
 
    constructor() {
 
        this.libs = {};
        this.versions = {};
        this.info = {};
    }
 
    /**
     * Search a directory for modules and add all
     *
     * @param $dir string
     * @param $sync bool
     *   Set to true if the method should run synchronically
     *   Default: false
     * @result Promise if $sync is false
     */
    addDir($dir, $sync) {};
 
    /**
     * Add an object directly
     *
     * @param $name string
     * @param $obj Object
     * @result bool
     *   Will be true if the object was added successfully
     *   And the object was not undefined
     */
    addMeta($name, $obj) {};
 
    /**
     * Add a module
     *
     * @param $path string
     * @param $sync bool
     *   Set to true if the method should run synchronically
     *   Default: false
     * @result Promise if $sync is false
     */
    addPath($path, $sync) {};
 
    /**
     * Read package.json and return the content
     *
     * @param $path string
     * @result Promise(Object)
     */
    getPackageInfo($path) {};
 
    /**
     * Attach event-listener to one of the following events.
     * - detect
     *     fired when a module was detected by addPath()
     *     handler: (moduleName, path) => {} 
     * - load
     *     fired when a module was loaded by addPath()
     *     handler: (moduleName, path, moduleObject, packageInfo) => {} 
     * - error
     *     fired when there was a module could not be loaded by addPath()
     *     handler: (moduleName, path, error) => {} 
     *
     * @param {string} $event 
     * @param {function} $handler 
     */
    on($event, $handler) {};
};

How To Use

You will first need to create a list of modules and meta-modules. The following code will use NML statically, which stores everything into the namespace _default

var nml = require('node-mod-load');
 
// Node Mod Load is able to read package information and return an object containing said information
var packageConfig = nml.getPackageInfo('./plugins/demo');
console.log('Plugin found: ' + packageConfig.name);
 
// Act on module events
nml.on('load', (modName, path, mod, info) => {
  console.log(`Loaded "${modname}" from "${path}" at version "${info.version}"`);
 
  // do sth. with the module
  mod.foo();
});
 
// This will add a single module or module-package to the list
// addPath will return a promise
nml.addPath('./some-module.js');
nml.addPath('./my-functionality');
 
// If you need addPath to be sync, just set the second parameter to true
nml.addPath('./somePackage', true);
 
// This will add all .js modules and all module-packages in the directory "./libs" to the list
// addDir used like this will return a Promise
nml.addDir('./libs');
 
// addDir can also be used as a sync function by adding a true as second parameter
nml.addDir('./modules', true);
 
// This will add a meta-module to the list
nml.addMeta('meta', { hellowWorld: () => { console.log('Hey there!'); } });

After building the list you can just require Node-Mod-Load anywhere and get the module from it

var libs = require('node-mod-load').libs; // <- the object `libs` will include everything you added
 
var hellowFun = () => {
  return libs.meta.hellowWorld();
};

Instead of using NML statically, you can also use namespaces to improve overview by a great deal and separate different parts of your application transparently in the code.
Please understand that due to Node.JS's nature, all modules can only be added once. If they are required a second time, they will be added from Node.JS's cache.

var nml = require('node-mod-load');
var myNamespacedNML = nml('myNamespace');
 
myNamespacedNML.addDir('./subMod/src');
myNamespacedNML.libs.foo('bar');
 
// The following will throw, even thought we might have added nml.libs.meta object with that particular method earlier
myNamespacedNML.libs.meta.hellowWorld();

When adding a module package (folder with package.json), the version may be retrived from the nml.versions object (depending on your namespace!)

console.log('Version of foo: ' + myNamespacedNML.versions['foo']);

License

MIT