dependable

Dependable

A minimalist dependency injection framework for node.js.

Example

Create a container

Create a new container by calling dependable.container:

var dependable = require('dependable'),
    container = dependable.container();

Register some dependencies

Register a few dependencies for later use (a string and an object):

container.register('occupation', 'tax attorney');
container.register('transport', {
  type: 'station wagon',
  material: 'wood-paneled'
});

Register a dependency that has other dependencies

When the argument is a function, the function's arguments are automatically populated with the correct dependencies, and the return value of the function is registered as the dependency:

container.register('song', function (occupation, transport, legalStatus) {
  var song = {};

  song.chorus = function chorus() {
    return [
      'I\'m a ' + occupation,
      'On a ' + transport.material + ' ' + transport.type + ' I ride',
      'And I\'m ' + legalStatus.message
    ].join('\n');
  };

  return song;
});

Register a dependency out-of-order

song depends on a legalStatus, which hasn't been registered yet. Dependable resolves dependencies lazily, so we can define this dependency after-the-fact:

container.register('legalStatus', {
  warrants: [],
  message: 'without outstanding warrants'
});

Resolve a dependency and use it

Like with container.register, the function arguments are automatically resolved, along with their dependencies:

container.resolve(function (song) {
  /*
   * I'm a tax attorney
   * On a wood-paneled station wagon I ride
   * And I'm without outstanding warrants
   */
  console.log(song.chorus());
});

Re-register dependencies

As it stands, song returns boring, non-catchy lyrics. One way to change its behavior is to re-register its dependencies:

container.register('occupation', 'cowboy');
container.register('legalStatus', {
  warrants: [
    {
      for: 'shooting the sheriff',
      notes: 'did not shoot the deputy'
    }
  ],
  message: 'wanted: dead or alive'
});

This is really useful in a number of situations:

1. A container can register configuration parameters for an application---for example, a port---and allows them to be changed later
2. Dependencies can be replaced with mock objects in order to test other dependencies

To resolve the updated dependencies, provide an empty override:

container.resolve({}, function (song) {
  /*
   * I'm a cowboy
   * On a wood-paneled station wagon I ride
   * And I'm wanted: dead or alive
   */
  console.log(song.chorus());
});

Override dependencies at resolve time

It's also possible to override dependencies at resolve time:

var horse = {
  type: 'horse',
  material: 'steel'
};

container.resolve({ transport: horse }, function (song) {
  /*
   * I'm a cowboy
   * On a steel horse I ride
   * And I'm wanted: dead or alive
   */
  console.log(song.chorus());
});

Sounds like a hit!

API

container.register(name, function) - Registers a dependency by name. function can be a function that takes dependencies and returns anything, or an object itself with no dependencies.

container.register(hash) - Registers a hash of names and dependencies. This is useful for setting configuration constants.

container.load(fileOrFolder) - Registers a file, using its file name as the name, or all files in a folder. Does not traverse subdirectories.

container.get(name, overrides = {}) - Returns a dependency by name, with all dependencies injected. If you specify overrides, the dependency will be given those overrides instead of those registered.

container.getSandboxed(name, overrides = {}) - Returns a dependency by name, with all dependencies injected. Unlike get, you must specify overrides for all dependencies. This can (and should) be used during testing to ensure a module under test has been competely isolated.

container.resolve(overrides={}, cb) - Calls cb like a dependency function, injecting any dependencies found in the signature. Like container.get, this supports overrides.

container.list() - Return a list of registered dependencies.

Development

Dependable is written in coffeescript. To generate javascript, run npm run prepublish.

Tests are written with mocha. To run the tests, run npm test.

License

MIT