ddproxy / awilix

Simple dependency injection container + helper utilities to facilitate wiring of modules

Awilix

Simple Inversion of Control (IoC) container for Node with dependency resolution support. Make IoC great again!

Installation

npm install awilix --save

Requires Node v4 or above, and possibly npm v3.

Quick start

Awilix has a pretty simple API. At minimum, you need to do 2 things:

• Create a container
• Register some modules in it

index.js

const awilix = require('awilix');

// Some module you want to access everywhere.
const database = require('./db');

// Create the container.
const container = awilix.createContainer();

// Register the database module as "db".
container.register({
  db: database
});

// Use it.
container.db.query('SELECT ...');

Awilix: a primer

So the above example is not very interesting though. A reasonably sized project has a few directories with modules that may (or may not) depend on one another.

You could just require them all in the correct order, but where's the fun in that? Nah, let's have Awilix auto-load our modules and hook them up to the container.

For this mini-tutorial, we will use a todos API as an example.

services/todosService.js

// A nice function that takes the container
// as the first argument, and any number of
// additional arguments.
function getTodos(container, searchText) {
  const todos = container.todos;
  return todos.getTodos({ searchText: searchText }).then(result => {
    // Do something useful with the result here.. Or not.
    return result;
  });
}

// Export it so we can test it.
module.exports.getTodos = getTodos;

// To make this module Awilix-compatible, we
// have to use a default export that looks like this:
module.exports.default = (container) => {
  // Expose this module as "todosService"
  container.register({
    todosService: container.bindAll({
      // The todosService has a getTodos function,
      // which needs the container to grab
      // it's dependencies when called.
      getTodos: getTodos
    })
  });
};

The first bit is pretty standard, apart from the container argument. We basically just treat it as an object that has all the stuff we need - in this case, a todos repository (exposed as todos). How this came to be, we will find out... right now!

repositories/todosRepository.js

// This example is written with ES6 import-export syntax,
// as well as ES6 classes just to demonstrate how that works.

export class TodosRepository {
  // We need a database object to query against
  // - we declare this in the constructor.
  // This is called "constructor injection".
  constructor(db) {
    this.db = db;
  }

  // Queries the DB for todos..
  getTodos(query) {
    return this.db.sql(`select * from todos where text like '%${query.searchText}%'`).then(result => {
      // Transform DB result to todos..
      return result.map(todo => {...});
    });
  }
}

// Since we are using constructor injection,
// we can't be sure if "container.db" is available yet,
// so we use the dependsOn API.
export default function (container) {
  // We depend on the module exposed as "db".
  container.dependsOn(['db'], () => {
    // When we get here, we know "db" is ready!
    // Register the repository as "todos".
    container.register({
      todos: new TodosRepository(container.db)
    })
  });
}

This time we used a class (instead of functions that take the container as the first argument), and so we used container.dependsOn to defer registration until the db module was ready.

For good measure, let's cover the database module as well.

db/db.js

// We require the provider here as registering
// it with the container won't be needed.
const someDbProvider = require('some-db-provider');

export function connect() {
  // Returns a promise...
  return someDbProvider.connect({
    host: 'localhost'
  });
}

export default function(container) {
  // We are returning a promise. Yes, this is supported.
  return connect().then(database => {
    container.register({
      db: database
    })
  });
}

Okay! We have written our modules, now we need to connect them.

In our app's main script (where we imported Awilix), we are going to load our modules. For clarity, I've included everything here.

index.js

const awilix = require('awilix');

// Create the container.
const container = awilix.createContainer();

// Load our modules.
container.loadModules([
  // Awilix uses `glob` to resolve modules.
  // If you've used `dependsOn` correctly, or just using
  // the functional aproach (e.g. `todosService.js`), the
  // ordering won't matter.
  'services/*.js',
  'repositories/*.js',
  'db/db.js'
]).then(() => {
  // Our container is ready! Start your server or whatever..
  // Most importantly, we can use our todos service!
  const todosService = container.todosService;

  todosService.getTodos('use awilix').then(todos => {
    // Success! To the pub!
    console.log(todos);
  });
});

Note how in getTodos, we did not specify the container as the first argument! The observant reader may have remembered that we used a little function called bindAll in todosService.js.

That's it for the mini-guide. Be sure to read the short API docs below so you know what's possible.

The Awilix Container Pattern (ACP)

So in the above example, you might have noticed a pattern:

module.exports = function(container) {
  container.register({
    someStuff: 'yay',
    someFunction: container.bind(someFunction),
    someObject: container.bindAll({
      moreFunctions: moreFunctions
    })
  })
}

This is what I refer to as the Awilix Container Pattern (ACP), and is what the loadModules API uses to let you register your stuff with the container in a "discovery-based" manner.

An ACP function MAY:

• return a Promise
• use container.dependsOn to declare dependencies up-front (see corresponding section)

API

The awilix object

When importing awilix, you get the following stuff:

• createContainer
• listModules
• AwilixResolutionError

These are documented below.

createContainer()

Creates a new Awilix container. The container stuff is documented further down.

listModules()

Returns a promise for a list of {name, path} pairs, where the name is the module name, and path is the actual full path to the module.

This is used internally, but is useful for other things as well.

Args:

• globPatterns: a glob pattern string, or an array of them.
• opts.cwd: The current working directory passed to glob. Defaults to process.cwd().
• returns: a Promise for an array of objects with:
  • name: The module name - e.g. db
  • path: The path to the module relative to options.cwd - e.g. lib/db.js

AwilixResolutionError

This is a special error thrown when Awilix is unable to resolve all dependencies (due to dependOn). You can catch this error and use err instanceof AwilixResolutionError if you wish. It will tell you what dependencies it could not find.

The AwilixContainer object

The container returned from createContainer has some methods and properties.

container.registeredModules

A hash that contains all registered modules. Anything in there will also be present on the container itself.

container.bind()

Creates a new function where the first parameter of the given function will always be the container it was bound to.

Args:

• fn: The function to bind.
• ctx: The this-context for the function.
• returns: The bound function.

Example:

container.one = 1;
const myFunction = (container, arg1, arg2) => arg1 + arg2 + container.one;

const bound = container.bind(myFunction);

bound(2, 3);
// << 6

container.bindAll()

Given an object, binds all it's functions to the container and assigns it to the given object. The object is returned.

Args:

• obj: Object with functions to bind.
• returns: The input obj

Example:

const obj = {
  method1: (container, arg1, arg2) => arg1 + arg2,
  method2: (container, arg1, arg2) => arg1 - arg2
};

const boundObj = container.bindAll(obj);
boundObj === obj;
// << true

obj.method1(1, 2);
// << 3

container.register()

Given an object, registers one or more things with the container. The values can be anything, and therefore are not bound automatically.

Args:

• obj: Object with things to register. Key is the what others will address the module as, value is the module itself.
• returns: The container.

Example:

const addTodo = (container, text) => { /* ...*/ };
const connect = container => awesomeDb.connect(container.DB_HOST);

container.register({
  // Any value goes.
  DB_HOST: 'localhost',
  // using bindAll
  todoService: container.bindAll({
    addTodo: addTodo
  }),
  // Not bound.
  log: function(text) {
    console.log('AWILIX DEMO:', text);
  },

  connect: container.bind(connect)
});

// Exposed on the container as well as `registeredModules`.
container.todoService === container.registeredModules.todoService;
// << true

container.todoService.addTodo('follow and start awilix repo');
console.log(container.DB_HOST);
// << localhost

container.log('Hello!');
// << AWILIX DEMO: Hello!

connect();

container.loadModules()

Given an array of globs, returns a Promise when loading is done.

Awilix will use require on the loaded modules, and call their default exported function (if it is a function, that is..) with the container as the first parameter (this is the Awilix Container Pattern (ACP)). This function then gets to do the registration of one or more modules.

Args:

• dependencies: Array of strings that map to the module being grabbed off the container - e.g. 'db' when using container.db.
• returns: A dependency token (an internal thing, don't mind this).

Example:

// repositories/todosRepository.js
class TodosRepository {
  constructor(dependencies) {
    // We save the reference here, so it *has* to exist at construction-time!
    this.db = dependencies.db;
  }
}

// We are not using any named exports, so we
// don't have to use module.exports.default.
module.exports = container => {
  container.dependsOn(['db'], () => {
    container.register({
      todos: new TodosRepository(container)
    })
  });
}

container.dependsOn()

Used in conjunction with loadModules, makes it easy to state up-front what your module needs, and then get notified once it's ready. This is useful for doing constructor injection where you grab the dependencies off the container at construction time rather than at function-call-time.

I recommend using the functional approach as it's less complex, but if you must, this method works perfectly fine as well. It's just a bit more verbose.

Args:

• dependencies: Array of strings that map to the modules being grabbed off the container - e.g. 'db' when using container.db.
• returns: A dependency token (an internal thing, don't mind this).

Example:

// repositories/todosRepository.js
class TodosRepository {
  constructor(dependencies) {
    // We save the reference here, so it *has* to exist at construction-time!
    this.db = dependencies.db;
  }
}

// We are not using any named exports, so we
// don't have to use module.exports.default.
module.exports = container => {
  container.dependsOn(['db'], () => {
    container.register({
      todos: new TodosRepository(container)
    })
  });
}

Contributing

Clone repo, run npm i to install all dependencies, and then npm run test-watch + npm run lint-watch to start writing code.

For code coverage, run npm run coverage.

If you submit a PR, please aim for 100% code coverage and no linting errors. Travis will fail if there are linting errors. Thank you for your considering contributing. :)

What's in a name?

Awilix is the mayan goddess of the moon, and also my favorite character in the game SMITE.

Author

Jeff Hansen - @Jeffijoe