Name: JavaScript & Node.js: Full-Stack JavaScript Development
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Introduction & Learning Goals

🎯 What You'll Learn

🌐 HTTP Protocol

Client-server architecture
Request/response cycle
Status codes & headers

⚡ JavaScript Core

Functions, objects & arrays
Async: Promises & async/await
Modern ES6+ syntax

🖥️ Browser APIs

DOM manipulation
Events & event handling
Fetch API & AJAX

🚀 Node.js

Server-side JavaScript
File system & modules
Building APIs

📚 Course Flow

HTTP Basics → JS Refresher → Browser → Node.js

Understand how the web works: clients, servers, and HTTP.
Refresh core JavaScript concepts and modern patterns.
Apply JavaScript in the browser (DOM) and on the server (Node.js).

Web Foundations: HTTP

Scenario

The initiator of an HTTP request is the client in that exchange. Your server can also call other servers (external APIs) — in that request, your server is the client. Client vs server describes who starts the request; client‑side vs server‑side describes where code runs.

👥 Understanding the Actors

Every HTTP request involves a client and a server

🔄 Roles per request

A client starts a request; a server answers. In chains (your server → external API) the roles switch per hop.

Why ports

One IP, many apps. The OS delivers packets to the process bound to the destination port.

DNS → IP

Resolve example.com to an IP (cached by TTL). CDNs often answer with a nearby edge.

Connect, then HTTP

TCP 3‑way → TLS (for HTTPS) → send request line + headers → receive response.

Advanced: routing & sockets

🔀

Reverse proxy routing

443 (Nginx) can route api.example.com → localhost:8000, www.example.com → localhost:3000, assets → localhost:9000.

🔌

Ephemeral client ports

Each connection is a 4‑tuple (clientIP:clientPort ⇄ serverIP:serverPort), e.g. 198.51.100.24:53214 ⇄ 203.0.113.10:443.

🌍

Anycast/CDN

One advertised IP maps to multiple edges; DNS and BGP steer you to a close POP.

Anatomy of HTTP Messages

A message = start line + headers + optional body. Each part has distinct semantics. Dive deeper for framing, wire format, and caching implications.

Status Codes: Semantics & Strategy

Status codes drive caching, retries, SEO, monitoring and auth flows before any body is read. Use precise codes consistently; guesswork costs performance.

Headers & Content Types (Quick View)

Headers = metadata; start line + headers often decide caching, routing, auth before body is read. Content type tells parsers how to treat the body.

🤝

NEGOTIATION

Accept

Content-Type

💾

CACHING

Cache-Control

ETag

validators

🔐

AUTH

Authorization

WWW-Authenticate

🍪

SESSION

Cookie

Set-Cookie

🗜️

COMPRESSION

Accept-Encoding

Content-Encoding

🔍

TRACE

Traceparent

X-Request-ID

📄

REPRESENTATION

JSON

HTML

multipart

binary

Communication Examples

GET Request

A simple GET request to fetch a list of users. The client specifies it accepts JSON responses.

GET /api/users HTTP/1.1
Host: example.com
Accept: application/json

POST Request

A POST request to create a new user. The body contains JSON data with the user's information.

POST /api/users HTTP/1.1
Host: example.com
Content-Type: application/json

{"name":"Mehdi","role":"student"}

Server Response

A successful response with caching headers, compression, and an ETag for future revalidation.

HTTP/1.1 200 OK
Date: Thu, 06 Nov 2025 10:11:12 GMT
Server: example-app
Content-Type: application/json; charset=utf-8
Cache-Control: max-age=60, public
ETag: "users:v1:af31b2"
X-Request-ID: 8b7c2f55-91d7-4e6a-8209-9f8a1f4c1c21
Content-Encoding: br

[{"id":1,"name":"Mehdi"},{"id":2,"name":"Ada"}]

Reading the response without the body: Status + headers already tell success, cacheability, compression, and revalidation strategy (ETag). Monitoring often ignores the body.

Anatomy of HTTP Messages

Start Line

GET /api/users HTTP/1.1

Method + Path + Version (request) or Version + Status + Reason (response)

Headers

Host: example.com
Accept: application/json
Authorization: Bearer ...

Key: Value pairs. Control caching, auth, content type, routing.

Empty Line

↵

CRLF separator between headers and body. Required.

Body

{"name":"Mehdi","role":"student"}

Optional. Format defined by Content-Type header. Can be JSON, HTML, binary, etc.

🔀

Intermediaries

Often ignore body for decisions

Rely on headers for caching/retries/compression

Message Examples

Framed Examples

GET /api/users?page=1 HTTP/1.1
Host: example.com
Accept: application/json

HTTP/1.1 200 OK
Content-Type: application/json; charset=utf-8
Cache-Control: max-age=60, public
ETag: "users:v1:af31b2"

[{"id":1,"name":"Mehdi"},{"id":2,"name":"Ada"}]

HTTP/1.1 200 OK
Content-Type: text/html; charset=utf-8
Cache-Control: max-age=120, public

<!doctype html>
<html>
  <head><title>Example</title></head>
  <body>
    <h1>Hello from the web server</h1>
    <!-- …rest of the page omitted… -->
  </body>
</html>

Legend: start line • headers • blank line • body. Tip: GET requests do not include a body; use query parameters or POST for complex searches.

Status Codes: Semantics

✅

2xx Success

200 OK

201 Created

204 No Content

206 Partial

↪️

3xx Redirect

301 Permanent

302 Temp

303 See Other

304 Not Modified

307/308 Preserve method

⚠️

4xx Client

400 Bad Request

401 Unauthorized

403 Forbidden

404 Not Found

409 Conflict

422 Unprocessable

429 Rate Limit

❌

5xx Server

500 Error

502 Bad Gateway

503 Unavailable

504 Timeout

Status Code Patterns (Design Guide)

Apply a consistent decision tree: (1) Did the request succeed? (2) If not, is the fault on the client (4xx) or server (5xx)? (3) Pick the most specific code; never tunnel errors through 200.

🔐

Auth vs Authorization

401 No/expired credentials → include WWW-Authenticate.

403 Credentials valid but action forbidden (scope/role).

Rule: Can supplying new credentials help? If yes → 401 else 403.

{
  "error":"forbidden",
  "required_role":"admin"
}

✓

Validation & Semantics

400 Malformed (parse/type error).

422 Well‑formed but domain rule failed.

409 Version / uniqueness / state conflict.

410 Resource intentionally removed (stop retrying).

{
  "error":"validation",
  "field_errors":[{"field":"email","issue":"already taken"}]
}

💾

Caching & Conditionals

200 Fresh; send ETag/Cache-Control.

304 Validator matched (If-None-Match/If-Modified-Since).

Rule: Always emit a strong validator for cacheable GETs.

GET /items
If-None-Match: "rev-27"
→ 304 Not Modified

🔄

Retries & Resilience

502 Upstream error (dependency failed).

503 Temporary overload / maintenance (add Retry-After).

504 Upstream timeout.

Retry only idempotent methods (GET, HEAD, OPTIONS, safe DELETE, some PUT).

HTTP/1.1 503 Service Unavailable
Retry-After: 120
{"error":"overloaded"}

⏱️

Rate Limiting

429 Too Many Requests (quota window exceeded).

Return: Retry-After, X-RateLimit-Remaining, X-RateLimit-Reset.

Rule: Use 429 (not 403) for transient quota exhaustion.

HTTP/2 429
Retry-After: 5
X-RateLimit-Remaining: 0
{"error":"rate_limit","retry_in":5}

📦

Bulk / Partial

207 Multi-Status (mixed results) OR

200 with per-item status objects.

Prefer 200 + array unless spec needs 207.

{
  "results":[
    {"id":1,"status":201},
    {"id":2,"status":409,"error":"duplicate"}
  ]
}

📥

Ranges / Downloads

206 Partial Content (serve byte range).

416 Invalid range request.

HTTP/1.1 206 Partial Content
Content-Range: bytes 0-1023/4096

🔁

Idempotent Mutations

PUT replace → 200 (return body) or 204 (no body).

PATCH partial update → 200/204; use 409 on version mismatch.

DELETE existing or already deleted → often always 204 to be idempotent.

📋

Error Envelope

Shape: { error, message?, details?, trace_id? }.

No stack traces in prod; supply correlation id.

Never use 200 with an error wrapper.

{
  "error":"conflict",
  "message":"Version mismatch",
  "expected_version":12
}

Decision Cheatsheet

Malformed JSON: 400
Business rule fail: 422
Concurrent update: 409
Missing auth: 401
Not allowed: 403
Over capacity: 503 + Retry-After
Rate limited: 429
Removed resource: 410

JavaScript Overview

⚙️ How JavaScript Works

📝

Your Code

.js files

→

🔧

JS Engine

V8, SpiderMonkey

→

⚡

Execution

Machine code

Single-Threaded

One task at a time

Event Loop

Handles async operations

ECMAScript

Language standard

Non-Blocking

Async I/O operations

Engines & the Language

JS engines (like V8, SpiderMonkey) implement the ECMAScript standard. JS is single‑threaded with an event loop; asynchronous work uses callbacks, promises, and async/await.

Core Concepts at a Glance

📦

Types & Variables

Primitives, type coercion, let/const, functions & arrow functions

string number boolean () =>

🏗️

Objects & Context

Object literals, prototypes, this binding, classes & constructor patterns

this bind class new

📊

Arrays & Iteration

Functional array methods, higher-order functions, transformations & reductions

map filter reduce sort

⚡

Errors & Async

Exception handling, promises, async/await, error propagation patterns

try/catch Promise async await

Deep dive in the Language Refresher.

Node.js Runtime

🚀 Node.js Architecture

📝 Your JavaScript Code

↓

🔧 Node.js APIs

fs, http, path, crypto...

↓

V8 Engine

JS execution

libuv

Async I/O

↓

💻 Operating System

Files, Network, Processes

Common Use Cases:

🌐 REST APIs ⚡ Real-time apps 💻 CLI tools 🔗 Microservices

Idea behind Node.js

Node.js runs JavaScript on the server using the V8 engine plus system bindings for files, network, and more. It’s great for I/O‑heavy apps.

Learn more

See the dedicated Node.js page for examples and patterns.

🚀 Ready to go deeper?

Continue to JavaScript Refresher

Strengthen your JavaScript fundamentals with modern ES6+ syntax, functions, objects, and async patterns.

📦 Variables & Types

⚡ Functions & Objects

🔄 Async & Promises

Explore JS Refresher

{ }

</>

DOM

Introduction & Learning Goals

🎯 What You'll Learn

📚 Course Flow

Web Foundations: HTTP

👥 Understanding the Actors

🔄 Roles per request

Why ports

DNS → IP

Connect, then HTTP

Anatomy of HTTP Messages

Status Codes: Semantics & Strategy

Headers & Content Types (Quick View)

Communication Examples

GET Request

POST Request

Server Response

JavaScript Overview

⚙️ How JavaScript Works

Engines & the Language

Core Concepts at a Glance

Types & Variables

Objects & Context

Arrays & Iteration

Errors & Async

Node.js Runtime

🚀 Node.js Architecture

Idea behind Node.js

Learn more

Continue to JavaScript Refresher

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