10 Quick TypeScript One-Liners

https://blog.bitsrc.io/10-quick-typescript-one-liners-128a2721345

https://javascript.plainenglish.io/18-javascript-one-liners-thatll-make-you-look-like-a-pro-678da78ccdb0

TS-Node: Typescript execute engine

In my previous article, I have described how to create a simple typescript nodejs project. The method works fine in a small project, but take longer compilation time on a large project because its need to compile all typescript files on every change.
Create Node.js & Express.js with Typescript Project

The solution is using ts-node where it direct run the typescript without compiling it to javascript.

1. Follow the steps to create a Node.js & Express.js with Typescript.
2. Type "npm install -g ts-node".
3. Add an entry to package.json.
   
     "scripts": {

       "test": "echo \"Error: no test specified\" && exit 1",

       "build": "tsc -b",

       "start": "node dist/app.js",

       "dev": "nodemon dist/app.js",

       "dev:ts": "nodemon --exec ts-node src/app.ts"

     },
4. Now you can just run the development using 1 console: npm run dev:ts

Create Node.js & Express.js with Typescript Project

Here are the steps to create Node.js & Express.js with Typescript Project.

1. Create a folder.
2. Type command "npm init" to create package files.
3. Type "npm install -g typescript" to install typescript.
4. Type "tsc --init" to create typescript config file.
5. Type "npm install express --save" to download express module.
6. Type "npm install nodemon --save-dev" to download nodemon developer tool.
7. Type "install install @types/node --save-dev" to download typescript node definition files.
8. Type "install install @types/express --save-dev" to download typescript express definition files.
9. Edit the package.json
10. Change to main to "dist/app.js" to point to the start javascript file.
11. Add the start scripts, "start" : "nodemon dist/app.js"
12. The package.json will look like below:
13. Edit the tsconfig.json
14. Add "moduleResolution" : "node" under "module" : "commonjs".
15. Change the "outDir" : "./dist". This is the location where typescript compiles the javascript.
16. Change the "rootDir" : "./srv". This is where we store the typescript files.
17. The tsconfig.json will look like below:
    
18. Create /src folder and add app.ts. Edit the app.ts with the below script.
    
    import express from "express";

    
    

    const app = express();

    const port = process.env.port || 3001;

    
    

    // Adding middleway to use syntax req.body.name.

    app.use(express.json());

    
    

    app.get("/", (req, res) => res.send("Hello World!"));

    
    

    app.listen(port, () =>

      console.log(`Example app is listening on post ${port}!`)

    );

    
    
19. Open a terminal run "npm start". This will start the web server using nodemon.
20. Open another terminal run "tsc --watch". This will watch the /src folder to compile the ts to javascript.
21. Call http://localhost:3001/ using postman. If you see "Hello World!", congratulation, you have completed the setup Node.js & Express.js with the Typescript project.
    
    

Below is the project you may download from GitHub.

https://github.com/htsiah/simple-rest-api-using-expressjs-with-typescript

Below GitHub is the example of the Node.js & Express.js project. You may compare the different of project setup.

https://github.com/htsiah/simple-rest-api-using-expressjs

Typescript: Shorthand Initialization

In a lot of use cases, the fields are initialized in the constructor.

class Person {

    // Fields declaration 

    name : string;

    private id : string;

    // Initial the field value in constructor

    constructor(name : string, id : string) { 

        this.name = name;

        this.id = id;

    }

}

You can simplify to

class Person {

    constructor(private name : string, public id : string) {}

}

Typescript: Singleton

 Singleton is a design pattern that ensures that only one objects exits.

/**

 * The Singleton class defines the `getInstance` method that lets clients access

 * the unique singleton instance.

 */

 class ExampleSingleton {

    private static instance: ExampleSingleton;

    /**

     * The Singleton's constructor should always be private to prevent direct

     * construction calls with the `new` operator.

     */

    private constructor() { }

    /**

     * The static method that controls the access to the singleton instance.

     *

     * This implementation let you subclass the Singleton class while keeping

     * just one instance of each subclass around.

     */

    public static getInstance(): ExampleSingleton {

        if (!ExampleSingleton.instance) {

            ExampleSingleton.instance = new ExampleSingleton();

        }

        return ExampleSingleton.instance;

    }

    /**

     * Finally, any singleton should define some business logic, which can be

     * executed on its instance.

     */

    public someBusinessLogic() {

        // ...

    }

}

/**

 * The client code.

 */

function clientCode() {

    const s1 = ExampleSingleton.getInstance();

    const s2 = ExampleSingleton.getInstance();

    if (s1 === s2) {

        console.log('Singleton works, both variables contain the same instance.');

    } else {

        console.log('Singleton failed, variables contain different instances.');

    }

}

clientCode();

Singleton used case can be logging class where we can re-use the object.