Factory Method Pattern Example

This project is an example of the Factory Method Pattern implemented in TypeScript. It includes a UserFactory class that creates instances of different user types.

This is one of my first projects in TypeScript, so I'm using it to learn the language and its features, as well as to practice design patterns.

What is the Factory Method Pattern?

The Factory Method Pattern is a creational design pattern that provides an interface for creating objects, but allows subclasses to alter the type of objects that will be created.

In this project, the UserFactory class provides a method getUser, which creates and returns instances of different user types based on the input key.

Installation

To install the project, you need to have Node.js and npm installed on your machine. Then, you can clone the repository and install the dependencies:

git clone
cd FactoryImplIdea
npm install

Install and Run from GitHub Artifact

Not really recommended, but still works thanks to webpack!

Go to https://github.com/CodeByAidan/Factory-Pattern/actions, then click on the most recent run, and click on (at the bottom) "Webpack Artifacts"

From there it will be downloaded, unzip the archive, and then you can cd to that folder, and run node index.js. It doesn't need any requirements, other than Node of course.

Building the Project

To build the project, you can run the following command:

npm run build

This will run webpack to create the entrypoint file in dist, bundle.js, and generate TypeScript definition files in the dist/types folder.

Running the Project

To run the project after building, simply run the following command:

npm run start

Running from the entrypoint file/Webpack bundle

If you want to run the project from the entrypoint file/Webpack bundle, you can run the following command:

node dist/bundle.js

or

npm run start

Running from transpiled TypeScript files (JavaScript)

If you want to run the project from the transpiled TypeScript files, you can run the following command:

Make sure you have run the build command before running this command:

npm run build:all

Then, you can run the following command:

node dist/js/index.js

Problems with running transpiled TypeScript files - FIXED!

After tsc is used to compile the TypeScript files, the import/export paths after TypeScript transpilation are not compatible with Node.js CommonJS module resolution...

I.e. import { UserService } from './service/userService'; becomes import { UserService } from './service/userService'; in dist/js/index.js...

You would think it would work fine when doing node dist/js/index.js but it doesn't...

aidan@localhost:~/projects/work/FactoryImplIdea$ node dist/js/index.js
node:internal/errors:496
    ErrorCaptureStackTrace(err);
    ^

Error [ERR_MODULE_NOT_FOUND]: Cannot find module '/aidan/FactoryImplIdea/dist/js/service/userService' imported from /aidan/FactoryImplIdea/dist/js/index.js
    at new NodeError (node:internal/errors:405:5)
    at finalizeResolution (node:internal/modules/esm/resolve:327:11)
    at moduleResolve (node:internal/modules/esm/resolve:980:10)
    at defaultResolve (node:internal/modules/esm/resolve:1193:11)
    at ModuleLoader.defaultResolve (node:internal/modules/esm/loader:403:12)
    at ModuleLoader.resolve (node:internal/modules/esm/loader:372:25)
    at ModuleLoader.getModuleJob (node:internal/modules/esm/loader:249:38)
    at ModuleWrap.<anonymous> (node:internal/modules/esm/module_job:76:39)
    at link (node:internal/modules/esm/module_job:75:36) {
  url: 'file:///aidan/FactoryImplIdea/dist/js/service/userService',
  code: 'ERR_MODULE_NOT_FOUND'
}

Node.js v18.19.0

aidan@localhost:~/projects/work/FactoryImplIdea$ echo "i'm going to lose it"
i'm going to lose it

So an alternative is doing node dist/js/index.js --experimental-specifier-resolution=node Stack Overflow Solution

But using --experimental-specifier-resolution=node is not a good solution because it is experimental and may not be supported in the future, as mentioned if you run it...

Another solution I personally found was adding "type": "module" to package.json and appending .js to every import statement in the transpiled JavaScript files.

So I made a script to do this for me in js-file-import-fixer.cjs and it is automatically ran after the build command in the build:all or build:types:js script in package.json.