ArchieJs introduction

Archiejs enforces the tenets of modular design on nodejs codebases.

• Strong encapsulation
• Well defined interfaces
• Explicit dependencies

ArchieJs is a dependency chaining library, for breaking up large nodejs projects into independent loosely coupled modules.

An Archiejs application is assembled together from interdependent modules, using recipes provided in json object. It's simpler than it sounds and great for maintaing a large codebase over a longer period of time.

The business logic is written in modules. Each module can provide for and consume from other modules. Isolation of a module is similar to java packages (for a comparision). A module also has a lifecycle, ie. they are initialized, provide services to their consumers and terminated (optional).

Read in more detail here: https://github.com/archiejs/archiejs-docs

Project Background

ArchieJs is derived from Architech.js (written by c9) and have several improvements. It is simpler, provides friendly error messages for novice users and is no longer an isomorphic nodejs framework.

The differences between ArchieJs and Archietect are as follows,

1. Removed support for browser execution.
2. Made it more usefriendly by adding more logs and friendlier error messages.
3. Added support for enhancers and new ways to define provides and consumes tags.
4. Added support for promises during module initialization sequence.

ArchieJs module semantics

It increases code reusablity, makes it easier to split the application into micro-services and visualize your webapp as a number of boxes and pipes connecting them (see provides and consumes below).

Each archiejs module has a package.json with a plugin field.

plugin: {
  provides: XXX,
  consumes: XXX
}

See test folder or demo apps for more details.

Plugin Interface

There are different ways to register a plugin/module interface. One of them is listed below. Others are explained in archiejs demo- applications and under the test folder.

// auth.js
 
/* All plugins must export this public signature.
 * @options is the hash of options the user passes in when creating an instance
 * of the plugin.
 * @imports is a hash of all services this plugin consumes.
 *
 * Returns
 * @returns one or more services provided/exported by the module
 */
 
module.exports = function setup(options, imports) {
 
  // "database" was a service this plugin consumes
  var db = imports.database;
 
  // Useful Tip :-
  // can throw an error, can return a Promise or
  // can return a value, as below
 
  return {
    // "auth" is a service this module provides
    auth: {
      users: function (callback) {
        db.keys(callback);
      },
      authenticate: function (username, password, callback) {
        db.get(username, function (user) {
          if (!(user && user.password === password)) {
            return callback();
          }
          callback(user);
        });
      }
    }
  };
};

Each module has a package.json file (see plugin key below).

{
    "name": "auth",
    "version": "0.0.1",
    "main": "auth.js",
    "private": true,
    "plugin": {
        "consumes": ["database"],
        "provides": ["auth"]
    }
}

If your archie module has multiple javascript files that provide services, there is a more convenient way of defining the same in package.json (see the demo- apps or test folders).

Archie main API

The Archiejs library exposes two functions as it's main API.

createApp(configObject)

This function starts an archie config. The config object is created using resolveConfig.

The return value is Promise with an Archie instance.

resolveConfig(configTree)

This is a sync function that creates a config object. It parses all the modules, reading their package.json's for the plugin key and creates the config object, used in createApp above.

Class: Archie

Inherits from EventEmitter.

The createApp function returns an instance of Archie.

Event: "service" (name, service)

When a new service is registered, this event is emitted on the app. Name is the short name for the service, and service is the actual object with functions.

Event: "plugin" (module)

When a module registers, this event is emitted.

Event: "error" (error)

When a plugin throws an error, the "error" event is emitted.