hekdi

node.js Dependency Injection

This module provides dependency injection for node.js

npm i hekdi

hekdi popular frameworks integration:

• Express
• Koa
• Hapi

Basic usage:

// imported.module.js
const { createModule } = require('hekdi');

class Dependency1 {
  constructor() {
    this.name = 'Dependency1';
  }
}

class Dependency2 {
  static get $inject() {
    return ['LocalDependency'];
  }

  constructor(d1) {
    this.name = 'Dependency2';
    this.d1 = d1;
  }
}

module.exports = createModule({
  name: 'ImportedModule',
  declarations: [
    { name: 'LocalDependency', strategy: 'singleton', value: Dependency1 },
    { name: 'PublicDependency', strategy: 'factory', value: Dependency2 },
    { name: 'Arr', strategy: 'value', value: [1, 2, 3] }
  ],
  exports: ['PublicDependency', 'Arr']
});

// main.module.js
const { createModule } = require('hekdi');
const importedModule = require('./imported.module');

class Ctrl {
  static get $inject() {
    return ['PublicDependency', 'Arr'];
  }

  constructor(publicDep, arr) {
    console.log(publicDep, arr);
  }
}

module.exports = createModule({
  name: 'SharedModule',
  declarations: [
    { name: 'Controller', strategy: 'singleton', value: Ctrl },
    { name: 'ControllerAs', strategy: 'alias', value: 'Controller' }
  ],
  imports: [ importedModule ]
})

// app.js
const { DI } = require('hekdi');
const MainModule = require('./main.module');
const di = DI.create();

di.bootstrap(MainModule);

const ctrl = di.resolve('ControllerAs');
// Dependency2 { name: 'Dependency2', d1: Dependency1 { name: 'Dependency1' } } [ 1, 2, 3 ]

Main concepts:

Top level API:

Top level api is DI class that bootstraps main module and serves dependencies from it then.

const { DI } = require('hekdi');
const di = DI.create();

di.module(moduleConfig) // creates new module from config

di.bootstrap(moduleConfig) // register module as main one and resolve dependencies from it

const dep = di.resolve('dependency') // return dependency that was registered to bootstrapped module according to its strategy

Modularity:

DI provides modules as a structural unit of app.

• declarations array sets own dependencies of this module.
• exports array tells what dependencies are available for other modules
• imports array will inject exported members from other module to this one

const { createModule } = require('hekdi');

createModule({
  name: 'SomeModule',
  declarations: [
    { name: 'LocalDependency', strategy: 'singleton', value: class X {} },
    { name: 'PublicDependency', strategy: 'factory', value: class Y {} },
    { name: 'Arr', strategy: 'value', value: [1, 2, 3] },
    { name: 'ZProvider', strategy: 'provider', value: () => ({ name: 'Z', strategy: 'factory', value: class Z {} })}
  ],
  exports: ['PublicDependency', 'Arr'], // if '*' set, module will export all of the dependencies including imported 
  imports: [ AnotherModuleInstance ]
});
// here 'LocalDependency' will be available for injection only for members of this module. 

Strategies:

• factory - each time a new instance will be created.
• singleton - only one instance will be created.
• value - just will be returned.
• constant - the same as value but can't be reassign.
• alias - used to create an alias for some dependency.
• provider - function that will be called, to get dependency config. Providers register dependencies before others do. Providers can't be exported from module.