Simple Dependency Injection for NodeJS

SDI is a simple dependency injection engine, inspired from Angular.

An example :

toto.js

exports.myFunction = function(a, $logger, $config) {
    $logger.info('toto ' + a + ' ' + $config);
}

To use it :

main.js

var sdi = require('sdi');
 
sdi.addToDefaultContext({
  $logger: {
    info: function(s) {
      console.log(s);
    }
  },
  $config: 'myParam',
});
 
sdi.require('./toto').myFunction('abc');
 

Output:

$ node main.js
toto abc myParam

Context

For dependency injection, you need a context. A context is simple a map of objects, keys have to start with $.

var myContext = {
  $a: require('fs')
};

If you specify no context, the default one is used.

You can add element to the default context with sdi.addToDefaultContext(myContext);

Use dependency injection on a full module :

var m = sdi.wrapModule(require('./myModule')); // use default context
var m = sdi.wrapModule(require('./myModule'), myContext); // use myContext as context
var m = sdi.wrapModule(require('./myModule'), myContext1, {$b: 2}); // use 2 contexts
var m = sdi.wrapModule(require('./myModule'), myContext1, sdi.defaultContext()); // use myContext and the default context
 
m.myFunc();
 

In a module loaded through dependency injection, you can inject $self to call methods on the same module using dependency injection.

exports.myFunc($logger) {
  ...
};
 
exports.myFunc2($logger, $self) {
  ...
  $self.myFunc();
};

Use dependency injection on single function :

function f(req, res, $logger, $component1, $component2) {
  ...
}
 
var ff = sdi.wrapFunction(f); // you can also provide a context, see above.
 
ff(req, res);

Use dependency injection on object :

function MyObj() {
}
 
MyObj.prototype.myFunc = function($logger) {
};
 
var o = sdi.wrapObject(new MyObj()); // you can also provide a context, see above.
o.myFunc();

You can inject $this in object, to access to call methods with dependency injection.

Using $this avoid to use .bind(this) on all sub functions.

MyObj.prototype.myFunc2 = function($logger, $this) {
  $this.myFunc();
};

Performances

Dependency resolution is only performed on the first function call. All subsequents calls are very fast (just few object moves).

Use dependency injection only for long running object. Avoid to use it on short live object (eg on object created in an http request).

Example : inject all the modules of a tools directory

main.js

var sdi = require('sdi');
 
sdi.addToDefaultContext({$logger: require('./tools/logger')});
sdi.addToDefaultContext({component1: require('./tools/component1')});
sdi.addToDefaultContext({component2: require('./tools/component2')});
 
sdi.require('my_app').run();

License

Copyright 2014 Bertrand Paquet

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.