Dependency Injection library for Node.js
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README.md

Spur: IoC

Dependency Injection library for Node.js.

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About the Spur Framework

The Spur Framework is a collection of commonly used Node.JS libraries used to create common application types with shared libraries.

Visit NPMJS.org for a full list of Spur Framework libraries >>

Topics

Features

  • Dependency injection (IoC) inspired by AngularJS
  • Auto injects folders
  • Ability to merge injectors
  • Ability to link injectors
  • Makes testing super easy
    • Ability to substitute dependencies in tests
  • Resolution of dependencies by querying via regular expression
  • Clear error stack trace reporting
  • Supports active Node versions in the LTS Schedule. (view current versions)

What is inversion of control and why you should use it?

Inversion of Control (IoC) is also known as Dependency Injection (DI). IoC is a pattern in which objects define their external dependencies through constructor arguments or the use of a container factory. In short, the dependency is pushed to the class from the outside. All that means is that you shouldn't instantiate dependencies from inside the class.

Inversion of control is used to increase modularity of the program and make it extensible, and has applications in object-oriented programming and other programming paradigms.

It allows for the creation of cleaner and more modular code that is easier to develop, test and maintain:

  • Single responsibility classes
  • Easier mocking of objects for test fixtures
  • Easier debugging in Node.js' async environment

Quick start

Installation

$ npm install spur-ioc --save

Usage

Here is a quick example that sets up the definition of an injector, some dependencies and a startup script.

src/injector.js

const spur = require('spur-ioc');

module.exports = function(){
  // define a  new injector
  const ioc = spur.create('demo');


  //register external dependencies or globals
  ioc.registerDependencies({
    '_'           : require('underscore'),
    'path'        : require('path'),
    'console'     : console,
    'nodeProcess' : process
  });

  // register folders in your project to be auto-injected
  ioc.registerFolders(__dirname, [
    'demo'
  ]);

  return ioc;
}

src/demo/Tasks.js

Example of file that depends on an injectable dependency. This example shows the usage of underscore (_).

module.exports = function(_){
    return _.map([1,2,3], function(num) {
        return 'Task ' + num;
    });
}

src/demo/TasksPrinter.js

This example injects Tasks and console dependencies, both previously defined in the injector.

module.exports = function(Tasks, console){
    return {
        print: function(){
          console.log(Tasks);
        }
    };
}

src/start.js (top declaration file)

Example of how to create an instance of the injector and start the app by using one of its dependencies.

const injector = require('./injector');

injector().inject(function(TasksPrinter){
  TasksPrinter.print();
});
Usage note for ES6 syntax

While it is tempting to utilize the fat arrow syntax in this top declaration file like the example below, it will not be supported by spur-ioc. For more information, read issue #26. Instead use the recommended approach above. There isn't a compelling reason to add that additional support. If you use this style, it will break as the report in issue #26.

const injector = require('./injector');

injector().inject((TasksPrinter) => {
  TasksPrinter.print();
});

Writing tests

Dependency injection really improves the ease of testing, removes reliance on global constiables and allows you to intercept seams and make dependencies friendly.

test/unit/TasksPrinterSpec.js

const injector = require('../../src/Injector');

describe('TasksPrinter', () => {
  beforeEach(function () {
    this.mockConsole = {
      logs:[],
      log: () => this.logs.push(arguments)
    };

    // below we replace the console dependency silently
    injector()
      .addDependency('console', this.mockConsole, true)
      .inject((TasksPrinter) => {
        this.TasksPrinter = TasksPrinter;
      });
  });

  it('should exist', function () {
    expect(this.TasksPrinter).to.exist;
  });

  it('should greet correctly', function () {
    this.TasksPrinter.print();
    expect(this.mockConsole.logs[0][0]).to.deep.equal([
        'Task 1', 'Task 2', 'Task 3'
    ]);
  });
});

Error reporting

One of the great things about ioc is that you get real application dependency errors upfront at the start of your application.

Missing dependency with typo

module.exports = function (TaskZ, console) {
  //...
}

// Produces:
// ERROR Missing Dependency TaskZ in  $$demo -> TasksPrinter -> TaskZ

Adding a cyclic dependency back to TasksPrinter in Tasks.js

module.exports = function (_, TasksPrinter) {
  //...
}

// Produces:
// ERROR Cyclic Dependency TasksPrinter in  $$demo -> TasksPrinter -> Tasks -> TasksPrinter

Contributing

We accept pull requests

Please send in pull requests and they will be reviewed in a timely manner. Please review this generic guide to submitting a good pull requests. The only things we ask in addition are the following:

  • Please submit small pull requests
  • Provide a good description of the changes
  • Code changes must include tests
  • Be nice to each other in comments. 😇

Style guide

The majority of the settings are controlled using an EditorConfig configuration file. To use it please download a plugin for your editor of choice.

Lint source code by running npm run lint.

All tests should pass

To run the test suite, first install the dependancies, then run npm test

$ npm install
$ npm test

License

MIT