depinj-express

An integration of depinj with express.

Usage

Installation npm install --save depinj-express

Example

import { Builder, Injector, ScopeType } from 'depinj-js';
import { toInjectedMiddleware } from 'depinj-express';
import { Router } from 'express';

class RequestsCounter {
  private track: number;

  constructor(initialState: number = 0) {
    this.track = initialState;
  }

  public increment(): void {
    this.track++;
  }

  public getValue(): number {
    return this.track;
  }
}

const incrementHandler = (counter) => (req, res, next) => {
  counter.increment();
  next();
}
const getValueHandler = (counter) => (req, res, next) => {
  res.json({ value: counter.getValue() });
  next();
}

// Registering instances
const builder = new Builder()
  .addType('RequestsCounter', RequestsCounter, [], ScopeType.SingleInstance)
  .add('IncrementingMiddleware', (_, inj) => incrementHandler(inj.getService('RequestsCounter')), ScopeType.Transient)
  .add('GetValueMiddleware', (_, inj) => getValueHandler(inj.getService('RequestsCounter')), ScopeType.Transient);

const registry = builder.build();

// Retrieving instances
const injector = new Injector(registry);
const counterHandler = toInjectedHandler(injector, 'IncrementingMiddleware');
const showCounterHandler = toInjectedHandler(injector, 'GetValueMiddleware');
const router = Router();

router.post('/counter', counterHandler);
router.get('/counter', showCounterHandler);

Check the example repository for more use cases.

How it works?

This works by injecting the dependency context to the express request, this means that it's the request that keeps the instances state. Also it ensures that the onScopeEnd function is called by binding it with the res.on('finish) event.

To inject a middleware to an Injector, all that's needed is for the middleware to be registered as a service, this means that the middleware needs to be in the Register. Once that is done, just call the function toInjectedHandler with the Injector instance and the service key. This function will return an express handler.

For error handlers, there's also a toInjectedErrorHandler function with similar behavior.