Verifying TypeScript Class Instances with Node Module Type Checking

Question

Verifying TypeScript Class Instances with Node Module Type Checking

My current task involves converting our Vanilla JS node modules to TypeScript. I have rewritten them as classes, added new functionality, created a legacy wrapper, and set up the corresponding Webpack configuration. However, I am facing an issue with singleton modules. Instead of exporting the class by default, we want to export a class instance as default. The problem arises when it comes to type checking:

import DebugJs from 'debug';
const test = (test: DebugJs) => {
    test.console('warn', 'does', 'respond', 'with a warning', test);
};

The issue is that DebugJs is not recognized as a type. Currently, I have to import an additional interface to properly set the type.

For comparison, this is what I currently do:

import DebugJs, { DebugJsInterface } from 'debug';
const test = (test: DebugJsInterface) => {
    test.console('warn', 'does', 'respond', 'with a warning', test);
};

I have tried experimenting with namespaces and module declarations. But being new to node module creation and TypeScript, I find myself unsure about my approach.

Here is my current setup in the index.d.ts file:

import DebugJs from './src/debugJsModule';
import {DebugLevels} from "./src/types/types";

export interface DebugJsInterface {
    levels:DebugLevels;
    enabled:boolean;
    level:number;
    console(...arguments: any): void;
    enableDebug(): void;
    disableDebug(): void;
    setLevel(level:number): void;
}

export interface Module {
    DebugJs: DebugJsInterface;
}

export default DebugJs;
declare module 'debug';

In this setup, DebugJsInterface serves as a workaround. It puzzles me because I thought index.d.ts should only contain type information. However, if I don't export the class instance here, my module import won't recognize it as a class properly.

My debugJsModule wrapper returns a class instance:

import DebugJs from './class/DebugJs';
import { DebugLevels } from 'debug/src/types/types';

const DebugJsInstance: DebugJs = new DebugJs();

export default DebugJsInstance;

The class itself is defined as a simple class and exported as a default export as well.

 class DebugJs { ... }

To clarify, all functionalities are working fine. My main goal is to understand how I can ensure the proper typing of my imported class instance using the same name (DebugJs) without relying on an extra imported interface as a workaround.

typescript node-modules

Answer 1

Answer №1

When it comes to organizing your code in a way that suits your preferences, one approach you can consider is keeping the class and singleton together in the same file. You can export the singleton as default and the class as a named export like this:

class DebugJs {
  // code
}

const debug = new DebugJs();

export default debug;
export {DebugJs};

Then, when you import the singleton in your client code:

import debug from '.../path';

debug.format().log().whatever(); // With proper typings and intellisense support, debug will be recognized as an instance of DebugJs.

If you ever need a fresh instance of DebugJs independent of the singleton, you can simply do:

import {DebugJs} from '.../path';

const debug = new DebugJs(); // Typing and intellisense will function correctly.

This pattern has been reliable for me in many cases, so I believe it should work well for your needs.

As for the issues you are facing with your current setup, it's hard to pinpoint the exact cause without more information. It could potentially relate to using default exports for types or combining that with the singleton re-export. Further debugging may be necessary to identify the root of the problem.

Answer 2

When it comes to organizing your code in a way that suits your preferences, one approach you can consider is keeping the class and singleton together in the same file. You can export the singleton as default and the class as a named export like this:

class DebugJs {
  // code
}

const debug = new DebugJs();

export default debug;
export {DebugJs};

Then, when you import the singleton in your client code:

import debug from '.../path';

debug.format().log().whatever(); // With proper typings and intellisense support, debug will be recognized as an instance of DebugJs.

If you ever need a fresh instance of DebugJs independent of the singleton, you can simply do:

import {DebugJs} from '.../path';

const debug = new DebugJs(); // Typing and intellisense will function correctly.

This pattern has been reliable for me in many cases, so I believe it should work well for your needs.

As for the issues you are facing with your current setup, it's hard to pinpoint the exact cause without more information. It could potentially relate to using default exports for types or combining that with the singleton re-export. Further debugging may be necessary to identify the root of the problem.

Answer 3

Answer №2

This code snippet may be confusing:

import DebugJs from 'debug';
const test = (test: DebugJs) => {
    test.console('warn', 'does', 'respond', 'with a warning', test);
};

The use of

an instance of an instance of DebugJs

in the TypeScript type declaration doesn't seem logical.

It seems odd to import an instance and not utilize it immediately after.

However, there is a way to achieve this if needed:

const test = (test: typeof DebugJs) => {
    test.console('warn', 'does', 'respond', 'with a warning', test);
};

You might consider one of these options instead:

Import only DebugJsInterface for type guarding purposes.
Do not require it as a function argument.

Example 1:

const test = (test: DebugJsInterface) => {
    test.console('warn', 'does', 'respond', 'with a warning', test);
};

Example 2:

const test = () => {
    DebugJs.console('warn', 'does', 'respond', 'with a warning', test);
};

You may find one of the alternatives more suitable for your needs.

Answer 4

This code snippet may be confusing:

import DebugJs from 'debug';
const test = (test: DebugJs) => {
    test.console('warn', 'does', 'respond', 'with a warning', test);
};

The use of

an instance of an instance of DebugJs

in the TypeScript type declaration doesn't seem logical.

It seems odd to import an instance and not utilize it immediately after.

However, there is a way to achieve this if needed:

const test = (test: typeof DebugJs) => {
    test.console('warn', 'does', 'respond', 'with a warning', test);
};

You might consider one of these options instead:

Import only DebugJsInterface for type guarding purposes.
Do not require it as a function argument.

Example 1:

const test = (test: DebugJsInterface) => {
    test.console('warn', 'does', 'respond', 'with a warning', test);
};

Example 2:

const test = () => {
    DebugJs.console('warn', 'does', 'respond', 'with a warning', test);
};

You may find one of the alternatives more suitable for your needs.

Verifying TypeScript Class Instances with Node Module Type Checking

Answer №1

Answer №2

Similar questions

Issues with rapid refreshing are arising in Vite while dynamically importing components with React and typescript

Exploring Mixed Type Arrays Initialization in Typescript using Class-Transformer Library

Implementing basic authentication with AWS Lambda and Application Load Balancer

Is there a way to ensure that in React (Typescript), if a component receives one prop, it must also receive another prop?

What is the best way for me to determine the average number of likes on a post?

Having trouble retrieving data in the service. Unable to subscribe to it from other components

Angular 2's one-of-a-kind singleton solution

Learn how to effortlessly move a file into a drag-and-drop area on a web page with Playwright

Transcompiling TypeScript for Node.js

How to use attributes in Angular 2 when initializing a class constructor

Tips for resolving the "Page Not Found" error in your NextJs application

angular 6's distinctUntilChanged() function is not producing the desired results

Despite setting the esModuleInterop flag, I am still encountering an error with default imports

Determine the type of sibling parameter

How can one change the data type specified in an interface in TypeScript?

What are the best practices for integrating Quill with Node.js and MongoDB?

Is there a way to prevent storing all dependencies in the node_modules subfolder when using ReactNative?

The values of object keys are printed in a random order

What is the best way to retrieve a property value from an object using the .find() method?

Removing background from a custom button component in the Ionic 2 navbar