Typescript Day 2 : Diving more into Types ad Setup with Express

Continuing my journey with typescript, I have learnt about the various types and basic usage with express to develop simple servers. I also got to explore the various types packages that are defined for typescript based development.

Production vs. Development Compilation

In production, TypeScript compiles to JavaScript in a separate folder. In development, real-time compilation and auto-reloading help preview changes faster.

Getting Started

Use the npm package ts-node for quick TypeScript execution. Install globally with:

npm install -g ts-node typescript

Or install locally for projects with:

npm install --save-dev ts-node typescript

tsconfig.json

It defines how TypeScript interprets the code. Start with basic options like noImplicitAny to enhance type checking. Type Safety

TypeScript enforces specific types for inputs, aiding in error prevention and editor-level assistance. Create types using the type keyword.

Return Type

Specify return types to ensure function behavior. Handle possible division by zero errors.

Unknown Type

unknown is flexible but needs narrowing for operations. It's not assignable to any without assertions.

Types for Packages

Find @types on npm for package types. Install with:

npm install --save-dev @types/package-name

Generics and Configuration

Utilize "generics syntax" and set configurations in tsconfig.json to shape your TypeScript environment.

Unused Variables

Handle unused variables with care. Prefixing with underscores can signal intent to the compiler.

Best Practices

Use import for module importing and adjust noUnusedParameters considering library-wide functions.

ts-node-dev

Consider using ts-node-dev for running your app during development. Install it using npm and then configure the script to use ts-node-dev using the following :

"scripts": {
    "ts-node": "ts-node",
    "start": "ts-node-dev index.ts"
  },

A simple server with typescript and express js that returns BMI :

import express from "express";
import { Request, Response } from 'express';
const app = express();

// test endpoint
app.get("/", (_req ,res)=>{
    res.send("<h1>PONG🤘🚀</h1>");
})
// test endpoint
app.get("/hello", (_req ,res)=>{
    res.send("<h1>Hello, Full Stack!🤘🚀</h1>");
})
// interfaces
interface ReqParams {
  /* Add something as needed */
}
interface ReqBody {
  /* Add something as needed */
}
interface Resbody {
  /* Add something as needed */
}
interface ReqQuery{
    height : number;
    weight : number;
}
type bmiData = "Underweight" | "Normal range" | "Overweight";
const bmiResult = (weight : number, height : number) : bmiData=>{
    const bmi : number = weight/(height*height);
    if(bmi<=18.4){
        return "Underweight";
    }
    else if(bmi>=18.5 &&  bmi<=24.9){
        return "Normal range";
    }
 	else return "Overweight";
}
app.get("/bmi", (req : Request<ReqParams, ReqBody, Resbody, ReqQuery>,res : Response)=>{
    const {height, weight} = req.query;
    if(isNaN(height) || isNaN(weight)){
        res.status(301).json({
            error : "Misformatted parameters"
        })
    }
    res.status(200).json({
        height,
        weight,
        bmi : bmiResult(weight,height/100)
    });
})
const PORT = 5000;
app.listen(PORT, ()=>{
    console.log("App listening on port : ",PORT);
})

I'm excited to explore more about TypeScript's dynamic power!