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A minimalist dependency injection framework for node.js

README.md

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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

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

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

Copyright (c) 2013 i.TV LLC

Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal 
in the Software without restriction, including without limitation the rights 
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell 
copies of the Software, and to permit persons to whom the Software is
 furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
 all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 THE SOFTWARE.

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