I'm using inversify with inversify-express-utils.

I have a quite usual inversify/express setup.

• Controller
  • Service
    • A module
      • B module

B module is a class that looks like this:

import { injectable } from 'inversify';
import SpellCorrector from 'spelling-corrector';

@injectable()
export class SpellCorrectorFactory {
  private corrector: any;

  constructor() {
    this.corrector = new SpellCorrector();
    this.corrector.loadDictionary();
  }

  public correct = (text: string): string => this.corrector.correct(text);
}

Now, the problem here is that as you can see in the constructor, I have this line of code:

this.corrector.loadDictionary()

This line takes over a second to execute. So basically it seems like the actual instance creation is happening when I @inject service B to service A So every time I make a request, the constructor of SpellCorrectorFactory is being executed, so the request takes over 1000ms instead of below 100ms.

How can I bind this class to inversify so that during binding the class is being instantiated and in the A module I have access to the instance which was created on app start, and not when I send a request to the express path?

Thanks in advance!

I'm using inversify with inversify-express-utils.

I have a quite usual inversify/express setup.

• Controller
  • Service
    • A module
      • B module

B module is a class that looks like this:

import { injectable } from 'inversify';
import SpellCorrector from 'spelling-corrector';

@injectable()
export class SpellCorrectorFactory {
  private corrector: any;

  constructor() {
    this.corrector = new SpellCorrector();
    this.corrector.loadDictionary();
  }

  public correct = (text: string): string => this.corrector.correct(text);
}

Now, the problem here is that as you can see in the constructor, I have this line of code:

this.corrector.loadDictionary()

This line takes over a second to execute. So basically it seems like the actual instance creation is happening when I @inject service B to service A So every time I make a request, the constructor of SpellCorrectorFactory is being executed, so the request takes over 1000ms instead of below 100ms.

How can I bind this class to inversify so that during binding the class is being instantiated and in the A module I have access to the instance which was created on app start, and not when I send a request to the express path?

Thanks in advance!

• javascript
• typescript
• express
• inversifyjs

Share Improve this question Follow asked Aug 6, 2020 at 22:44 matewilkmatewilk 1,30111 gold badge1515 silver badges2929 bronze badges 16

• 1 I've never used it, but a cursory glance at their documentation indicates support for both singleton registrations and asynchronous factories. The latter is a rare feature in IOC containers. More to the point, why aren't you injecting SpellCorrector? As it is, your direct creation of that dependency nullifies the benefits of using such a framework – Aluan Haddad Commented Aug 7, 2020 at 4:06
• 1 When you say "bind", do you mean setter injection? If so it's a bad practice. What I am talking about is constructor injection: constructor(@inject(SpellCorrector) corrector: SpellCorrector) {}. It's an interesting framework, but I'm new to it as well. How does loadDictionary work? It should return a Promise. If you are performing synchronous IO, you must stop. JavaScript applications are single-threaded. If it returns a Promise, you can register an asynchronous provider in inversify. – Aluan Haddad Commented Aug 7, 2020 at 9:10
• 1 Yes, it does make sense. However, since constructors are synchronous, and since you say that takes loadDictionary takes 1000+ms, blocking startup. I am asking you how loadDictionary works. Is it performing synchronous IO? – Aluan Haddad Commented Aug 7, 2020 at 9:31
• 1 It matters a lot. If it is an async IO operation, then your SpellCorrectorFactory is in an initially invalid state when it is created, because of how you construct it. – Aluan Haddad Commented Aug 7, 2020 at 9:43
• 1 That it uses fs.readFileSync is terrible. JS is single threaded. That means that your application is 100% frozen, unable to do anything else while the file is loading. If it were properly written, it would use fs.promises.readFile. Then you could register it as a singleton, provided by an async factory, in inversify as documented here, solving all. Seriously though, I cannot overstate how problematic sync IO is in a JS application, client or server, except CLI tools. – Aluan Haddad Commented Aug 7, 2020 at 10:04

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1 Answer 1

Sorted by: Reset to default 5

Ok, just in case someone looks at this page in search for an answer.

The solution is as simple as:

container
  .bind<SpellCorrectorFactory>(TYPES.SpellCorrector)
  .to(SpellCorrectorFactory)
  .inSingletonScope();

This calls the constructor of the SpellCorrectorFactory immediately and returns the instance. So whenever you inject the result of this binding you have direct access to the instance and its functions.