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Mohin Sheikh
Mohin Sheikh

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JavaScript Learning Journey From Basics to Advanced

#webdev #javascript #beginners #programming

The course in four parts: basics, building blocks, real programs and async JavaScript, followed by the Node.js course

Most JavaScript tutorials are written for the browser: buttons, forms and the DOM. If you want to become a backend developer, much of that is not what you need first.

JavaScript: Basics to Advanced is a free course that teaches the JavaScript language for backend work. In 25 sessions it takes you from your first console.log() to promises, async/await and calling APIs with fetch. Everything runs in Node.js, and every example has been tested.

GitHub logo mohin-sheikh / javascript-basics-to-advanced

A structured JavaScript practice repository covering everything from variables and loops to closures, async programming, and ES6+ features. Designed to help you learn by doing with practical examples and exercises.

JavaScript: Basics to Advanced

A free, beginner-friendly JavaScript course for future backend developers. 25 sessions take you from your first console.log() to promises, async/await and calling APIs with fetch. Everything runs with Node.js, and every example is tested.

Sessions Tested on Node.js 24 Tested examples Animated diagrams Interview questions Free

The course in four parts: basics, building blocks, real programs and async JavaScript, followed by the Node.js course

Table of Contents

What Makes This Course Different
Backend from day one No web pages, buttons or browser code. You run everything with node file.js in a terminal, with examples from real servers: users, orders, carts, logins and APIs.
Every example is tested 587 example files were run on Node.js 24. The output in each session is the real output, so you can compare it with
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What Makes This Course Different

  • Backend from day one. There are no web pages or browser code. You run every example with node file.js, and the examples come from real servers: users, orders, carts, logins and APIs.
  • Every example is tested. 587 example files were run on Node.js 24. The output shown in each session is the real output, so you can compare it with yours line by line.
  • Learn by seeing. 319 animated diagrams show what happens inside your program: variables, the call stack, closures, the event loop and promises.
  • Learn from mistakes. 266 common beginner mistakes, each with the wrong code, what goes wrong and the fix.
  • Practice and interview prep. 199 practice exercises and 337 interview questions with answers.
  • One idea at a time. A session only uses what earlier sessions taught. Nothing appears before it has been explained.

Who It Is For

  • Complete beginners who have never written a line of code
  • Anyone who wants to become a backend or full-stack developer
  • Frontend developers who use JavaScript every day but never learned how it really works
  • Anyone preparing for a JavaScript or Node.js interview

You need a computer (Windows, macOS or Linux), Node.js 22 or newer, and a code editor such as VS Code. No programming experience is needed.

Course Outline

Part 1: Basics

The building blocks of every program: values, decisions and repetition.

# Session You will learn
01 Introduction to JavaScript What JavaScript and Node.js are, setting up, your first program, reading errors
02 Variables and Comments let, const, var, naming rules and comments
03 Data Types The 8 data types, typeof, null and undefined
04 Operators Arithmetic, comparison, === vs ==, logical operators and ??
05 Type Conversion Number(), parseInt(), truthy and falsy, safe input handling
06 Conditionals if, else if, switch, the ternary operator, validation
07 Loops for, while, do...while, for...of, break and continue
08 Strings and Template Literals Template literals, escape characters and string methods
09 Numbers and Math Decimals, money in paise, rounding, Math methods and random numbers

Part 2: Building Blocks

Organising code and data: functions, arrays, objects and classes.

# Session You will learn
10 Functions Parameters, return, default values, arrow functions, the call stack, recursion
11 Callbacks and Higher-Order Functions Callbacks, function factories, setTimeout and error-first callbacks
12 Arrays and Array Methods push, splice, map, filter, reduce, find, sorting, split and join
13 Objects Properties, nested objects, ?., Object.keys, arrays of objects
14 Destructuring, Spread and Rest Unpacking arrays and objects, copies and merges with ..., rest parameters
15 Shallow and Deep Copy References, shallow copies, structuredClone, shared-data bugs on a server
16 Scope, Hoisting and Closures The scope chain, var vs let, hoisting, the temporal dead zone, closures
17 this, Constructors and Classes this, new, classes, private fields, getters, static and extends

Part 3: Real Programs

What every real backend program needs: error handling, data formats, collections, and code split into files.

# Session You will learn
18 Error Handling try, catch, finally, throw, custom error classes, status codes
19 JSON and Dates JSON.stringify, JSON.parse, invalid JSON, dates, time zones, date math
20 Map and Set Map, Set, removing duplicates, caches and set operations
21 Modules require, module.exports, ES modules with import/export, project structure

Part 4: Async JavaScript

How one Node.js thread serves many users: waiting without blocking.

# Session You will learn
22 Timers setTimeout, setInterval, retries with backoff, debouncing, timeouts
23 The Event Loop The call stack, queues, microtasks, blocking code and the thread pool
24 Promises Creating promises, then/catch/finally, chaining, Promise.all, race, any
25 async/await and fetch async functions, await with try...catch, parallel tasks, calling APIs with fetch

A Look Inside

Every session explains the hard parts with animated diagrams. Here are three of them.

Session 23: the event loop, explained as a restaurant

One cashier takes orders while the kitchen cooks in the background, like the event loop

Session 24: the three states of a promise

A promise starts pending and becomes fulfilled or rejected, and then never changes

Session 25: what happens during a fetch call

fetch sends a request to an API, then reads the status and the JSON body with two awaits

What Every Session Contains

Part of a session What it gives you
Short sections One idea at a time, in simple words, with tables for quick review
Tested code examples A file name, the code, and the real output
Animated diagrams A picture of what happens while the code runs
Mini examples One or two small backend programs that combine the session's topics
Beginner mistakes The wrong code, the real error, and the correct code
Practice exercises Tasks to do on your own
Interview questions Short questions with clear answers, to check yourself

Plan for 1 to 2 hours per session, including the exercises. At one session a day, most learners finish in 4 to 5 weeks.

Start in Five Minutes

1. Install Node.js (the LTS version from nodejs.org) and check it in a terminal. Any version from 22 up works.

node -v
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v24.19.0
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2. Make a practice folder called js-practice and open it in VS Code (File > Open Folder).

3. Create a file called hello.js in that folder.

console.log("Hello, JavaScript!");
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4. Run it in the VS Code terminal (Terminal > New Terminal).

node hello.js
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Hello, JavaScript!
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That is how you run every example in the course. Now open Session 01.

How to Study

  1. Go in order. Each session builds on the ones before it. The links at the bottom of every session take you to the next one.
  2. Type the code yourself. Don't copy and paste. Typing teaches you the syntax, and your own typos teach you to read error messages.
  3. Run it and compare. Every example shows its exact output. If yours is different, find out why before you move on.
  4. Break things on purpose. Change a value or delete a line, predict what will happen, then run it.
  5. Finish each session. Read the beginner mistakes, do the exercises, and answer the interview questions out loud before you look at the answers.

When You Get Stuck

  • Read the error message. Node.js shows the file name, the line number and the exact place of the problem. Session 01 teaches you how to read it.
  • Compare your output with the output in the session, line by line.
  • Check the beginner mistakes at the end of the session. Your bug is often already there.
  • Search the exact error message online. Someone has almost always seen it before.
  • Take a break. A problem that looks impossible tonight is often easy tomorrow.

Study Tips

  • Code a little every day. 30 minutes daily beats 5 hours once a week.
  • Keep short notes in your own words, especially of the mistakes you made.
  • Explain each concept out loud, as if you were answering an interview question.
  • Go back to earlier sessions whenever a new one feels hard. That is part of learning, not a step back.

Find a Topic Fast

Revising for an interview? Jump straight to a topic.

Topic Session
let vs const vs var 02, 16
== vs === 04
Truthy and falsy values 05
Why 0.1 + 0.2 is not 0.3 09
map, filter and reduce 12
Copying objects without bugs 15
Closures and hoisting 16
this and classes 17
Custom errors and try...catch 18
require vs import 21
The event loop and microtasks 23
Promises, Promise.all and Promise.race 24
async/await and fetch 25

The README has the full list.

What You Will Be Able to Do

  • Write, run and debug JavaScript programs with Node.js
  • Read error messages and stack traces, and fix the cause
  • Work with strings, numbers, arrays and objects the way backend code does: input checks, money in paise, lists of users and orders
  • Organise code with functions, classes and modules
  • Handle errors cleanly and turn them into the right HTTP status codes
  • Explain closures, this, the event loop and promises in an interview
  • Write asynchronous code with async/await, and call other servers with fetch

What Comes Next: Node.js

This course teaches the JavaScript language. The Node.js course uses it to build real servers, REST APIs with Express, and databases with MongoDB, in 30 more sessions. Both courses use the same style and the same examples, so the step from one to the other is small.

Help It Reach More Learners

If this course helps you, please star the repository on GitHub so others can find it too. Found a mistake, or a part that is hard to understand? Open an issue. Every report helps the next learner.

Which JavaScript topic did you find hardest when you started? Tell me in the comments.

Start with Session 01: Introduction to JavaScript

Author: Mohin Sheikh. Follow me on GitHub for more free courses and updates.

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