Install & First Server
Express install karne ke liye pehle EK npm project chahiye: "npm init -y" package.json banata hai, phir "npm install express" Express ko node_modules mein laata hai aur dependencies mein likh deta hai.
Server tab tak REQUESTS NAHI SUNTA jab tak app.listen(PORT) call na ho. listen() EK PORT par bind karta hai aur EK optional callback deta hai jo server ready hone par chalta hai — agar port pehle se busy ho to EADDRINUSE error aata hai.
npm init -y
npm install express
# app.js
const express = require("express");
const app = express();
const PORT = process.env.PORT || 3000;
app.get("/health", (req, res) => res.json({ status: "ok" }));
app.listen(PORT, () => console.log(`Listening on ${PORT}`));- npm init -y + npm install express = project setup
- app.listen(PORT) ke bina server koi request nahi sunta
- PORT hamesha process.env.PORT se lo, fallback ke saath
"npm init -y" default package.json banata hai, "npm install express" Express ko dependencies mein add karta hai, aur nodemon (dev dependency) file change hone par server auto-restart kar deta hai — har baar manually restart karne ki zaroorat nahi.
npm init -y
npm install express
npm install --save-dev nodemon
// package.json
"scripts": { "dev": "nodemon server.js", "start": "node server.js" }app.listen() ke andar Express http.createServer(app).listen() hi call karta hai. Agar port pehle se use mein ho to EADDRINUSE error aata hai — ya to purana process band karo, ya alag port do. Listen ka return value ek http.Server hai, jise graceful shutdown ke liye rakha ja sakta hai.
const server = app.listen(PORT);
process.on("SIGTERM", () => {
server.close(() => console.log("Server band, ab process exit"));
});