Folder Structure and file contents are given below.

- node_modules
- utils
  - common.ts
- index.ts
- nodemon.json
- package-lock.json
- package.json
- tsconfig.json

tsconfig.json

{
  "compilerOptions": {
    "target": "es2016",                                 
    "lib": ["es2020", "dom"],
    "module": "commonjs",                               
    "outDir": "./dist",
    "esModuleInterop": true,                             
    "forceConsistentCasingInFileNames": true,           
    "strict": true,                                      
    "skipLibCheck": true                                 
  },
  "exclude": [
    "node_modules"
  ]
}

package.json

{
  "name": "ts-node-mon",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "watch" : "tsc --watch",
    "start": "node dist/index.js",
    "dev": "nodemon"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
    "express": "^4.19.1"
  },
  "devDependencies": {
    "typescript": "^5.4.3",
    "@types/express": "^4.17.21",
    "nodemon": "^3.1.0"
  }
}

nodemon.json

{
  "watch": ["**/*.ts"],
  "ext": "ts",
  "exec": "node dist/index.js"
}

index.ts

import express, { Express, Request, Response } from "express";
import { returnString } from "./utils/common";

const app: Express = express();

app.get("/", (req: Request, res: Response) => {
  const result = returnString();
  res.send(result);
});

app.listen(8000, () => {
    console.log(`Server is running at http://localhost:8000`);
});

utils/common.ts

export const returnString = (): string => {
  return "Response String";
};

After setting up the project folder and installing node modules, Run the following commands one by one.

1. tsc (All .js files will be created in dist folder as given in the tsconfig.json file)

2. Open one terminal and run the command npm run watch

3. Open another terminal and run the command npm run dev

With these steps, a development environment is established where modifications to TypeScript files trigger automatic transpilation to JavaScript, and the server reflects these changes in its responses.

Github code: https://github.com/Krius2023/nodemon-in-typescript