javascript-dependency-injection

Javascript Dependency Injection library

DI makes classes accessible by a contract. Instances are created when requested and dependencies are injected into the constructor, facilitating lazy initialization and loose coupling between classes.

As an example, consider a User and Persitance classes:

function WebSql(name, fieldList)  {
    this.persist = function (obj) {
        console.log('WebSQL will persist:');
        fieldList.forEach(function (field) {
            console.log('    ' + field + ': ' + obj[field]);
        });
    }
}

function IndexDB(name, fieldList)  {
    this.persist = function (obj) {
        console.log('IndexDB will persist:');
        fieldList.forEach(function (field) {
            console.log('    ' + field + ': ' + obj[field]);
        });
    }
}

function User(email, passwd, storage, role) {    // the `storoge` parameter holds an instance
    this.email = email;
    this.passwd = passwd;
    this.role = role;

    this.save = function () {
        storage.persist(this);
    };
}

With these classes in our pocket its time to setup the relations between them. The function that does this has the following signature

 function (<contract name>, 
           <class reference>, 
           [optional list of constructor arguments], 
           {optional configuration object} ) 

Or just in code:

var di = new DI();

di.register('user', User, [null, 'welcome', 'websql', 'nobody']);
di.register('websql', WebSql, ['userTable', ['email','passwd', 'role']], {singleton: true});
di.register('indexdb', IndexDB, ['userTable', ['email','passwd', 'role']], {singleton: true});

Note that the provied constructor arguments are default values or contract names. From now it is easy to create instances:

var user1 = di.getInstance('user', ['[e-mail]']),
        -> email: '[e-mail]', passwd: 'welcome', storage : WebSQL instance, role: 'nobody'
    user2 = di.getInstance('user', ['[e-mail]', 'newSecret']); // define a new password
        -> email: '[e-mail]', passwd: 'newSecret', storage : WebSQL instance, role: 'nobody'
        
if (user1 instanceof User) { /* user1 is an instance of User!! */ }

But it is also possible to use IndexDB as the persistance class:

var user = di.getInstance('user', ['[e-mail]', null, 'indexdb']),               // The password is set to null too!
        -> email: '[e-mail]', passwd: null, storage : IndexDB instance, role: 'nobody'
    root = di.getInstance('user', ['[e-mail]', undefined, 'indexdb', 'admin']); 
        -> email: '[e-mail]', passwd: 'welcome', storage : IndexDB instance, role: 'admin'

Checkout more detailed the documentation here

Gulp tasks

Install the dependencies as follows

$> npm install

To minify the library

$> gulp

To run the tests

$> gulp test

Installation

$> bower install javascript-dependency-injection