HTTP requests in Express

What

Express.js provides a convenient abstraction layer over raw HTTP a Node.js server:

• Handles incoming HTTP requests automatically
• Provides simple methods to define routes and responses
• You don’t write raw HTTP - Express parses it for you

• HTTP Fundamentals
• Express.js

Express Route Handlers

Express translates HTTP methods into JavaScript functions:

// GET request handler
app.get("/", (req, res) => {
  console.log(req.rawHeaders);  // Express gives you parsed request data
  res.send("<h1>Hello</h1>");   // Express handles response formatting
});
 
// POST request handler  
app.post("/", (req, res) => {
  res.sendStatus(201);  // Express method to send status codes
});

• Express enhances the basic HTTP request/response with useful properties:
  • req.rawHeaders - Express-parsed header data
    • rawHeaders = list of key/value pairs that come from where the request originated
      • ex. Google Chrome, Windows, localhost:3000, etc etc
  • res.send() - Express method to send responses
  • res.sendFile() - Express method to send files
  • res.sendStatus() - Express method to send status codes
• request comes in from the browser, and is sent to a specific URL or route on the server

Endpoints

Endpoints = specific URL paths your Express server responds to

• Each endpoint is a “route” in your application where a specific action is performed based on the request method (GET, POST, PUT, DELETE, etc.).
• Express makes it easy to define multiple endpoints:

app.get("/", (req, res) => {
  res.sendFile(__dirname + "/public/index.html");
});
 
app.get("/about", (req, res) => {
  res.send("<h1>This is the about page!</h1>");
});

• / → localhost:3000/
• /about → localhost:3000/about

app.get("/about", (req, res) => {
  res.send("<h1>This is the about page!</h1>");
});

Dynamic File path

• using res.sendFile → requires exact path

import { dirname } from "path";
import { fileURLToPath } from "url";
const __dirname = dirname(fileURLToPath(import.meta.url));
 
app.get("/", (req, res) => {
  res.sendFile(__dirname + "/public/index.html");
});

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Summary

1. HTTP = The universal protocol/language (HTTP Fundamentals)
2. Express = A Node.js framework that implements HTTP in JavaScript

Key Distinction

• HTTP methods (GET, POST, etc.) are the what - universal concepts
• Express handlers (app.get(), app.post(), etc.) are the how - JavaScript implementation

Quick Reference

• HTTP (Universal)
  • Methods: GET, POST, PUT, PATCH, DELETE
  • Status codes: 200, 404, 500, etc.
  • Request structure: Method + URL + Headers + Body
• Express (JavaScript Implementation)
  • Route handlers: app.get(), app.post(), etc.
  • Response methods: res.send(), res.sendFile(), res.sendStatus()
  • Request object: req.headers, req.body, etc.