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', ['[email protected]']),
-> email: '[email protected]', passwd: 'welcome', storage : WebSQL instance, role: 'nobody'
user2 = di.getInstance('user', ['[email protected]', 'newSecret']); // define a new password
-> email: '[email protected]', 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', ['[email protected]', null, 'indexdb']), // The password is set to null too!
-> email: '[email protected]', passwd: null, storage : IndexDB instance, role: 'nobody'
root = di.getInstance('user', ['[email protected]', undefined, 'indexdb', 'admin']);
-> email: '[email protected]', 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
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