hekdi

node.js Dependency Injection

Scale your node.js app with ease.

npm i hekdi

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: 'service', 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: 'service', value: class Y {} },
    { name: 'Arr', strategy: 'value', value: [1, 2, 3] }
  ],
  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:

• service - each time a new instance will be created with new keyword.
• factory - return the result of plain function call.
• 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.

Koa.js usage:

hekdi can be integrated with koa.js.

The main concept of framework integration is monkey patching of functions that are responsible for requests handling.

While using koa hakdi monkey patches use method.

Basic usage:

const Koa = require('koa');
const { koaDI } = require('hekdi');
const app = new Koa();

const moduleToBootstrap = {
  name: 'MainModule',
  declarations: [
    { name: 'ctrl', strategy: 'singleton', value: SomeClass },
    { name: 'echo', 
      strategy: 'value', 
      value: async (ctx) => {
         ctx.body = ctx.request.body;
      }
    }
  ],
  exports: '*'
};

koaDI(moduleToBootstrap, app);
// now di is already bootstrapped and ready to work. 
// In koa app you can reach di as `app.context.di`
// In di you can get koa app as `App` dependency.
app.use({
  controller: 'ctrl', // if dependency is object
  action: 'middleware', // you tell which of its methods will be called
  params: [1, 2, 3] // also you can pass additional params to call if needed
});

app.use({ action: 'echo' }); 
// you can reach some function without class creation by passing only action
// to `use` method

app.use(async (ctx) => { // you still can pass function to `use` method
  ctx.body = ctx.request.body;
});

app.listen(3000)

Usage with router

While using router the story is almost the same:

'use strict';

const Koa = require('koa');
const Router = require('koa-router');
const bodyParser = require('koa-body-parser');
const { koaDI } = require('hekdi');

const app = new Koa();
const router = new Router();

const moduleToBootstrap = {
  name: 'MainModule',
  declarations: [
    { name: 'ctrl', strategy: 'singleton', value: SomeClass },
    { name: 'echo', 
      strategy: 'value', 
      value: async (ctx) => {
         ctx.body = ctx.request.body;
      }
    }
  ],
  exports: '*'
};

koaDI(moduleToBootstrap, app, router);

app.use(bodyParser());

router
  .post(['/', '/test'], { action: 'echo'})
  .get('/', {
    controller: 'ctrl',
    action: 'getHandler',
    params: [1, 2, 3]
  }).get('/test', async (ctx) => {
    ctx.body = 'handled';
  });

  app
    .use(router.routes())
    .use(router.allowedMethods());

  app.listen(3000);