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JavaScript: Foundations to Fluency

16 lessons · Beginner · No account needed · Free forever

🌐 Browser & Node.js ⚡ Live editors 📖 Official sources only 🧠 Why before how

JavaScript is the language of the web — it runs in every browser and on servers via Node.js. This course takes you from complete beginner to writing real programs, one concept at a time. Every line of code is explained in plain English. Every page has a live editor — run the code and see the output immediately.

The most important lesson comes early: === vs == (Lesson 8). Understanding the difference prevents more bugs than almost anything else in JavaScript.

🚀 Stage 1 — Getting Started 2 lessons ▾

What JavaScript is, where it runs, and how to write and execute your first programs.

1
What is JavaScript
What JS is, where it runs, browser vs Node.js — the two homes.
orientation
→
2
Setup & Running
Browser console, script tags, Node.js install, the REPL.
environment
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⚙️ Stage 2 — Core Language 7 lessons ▾

The building blocks: syntax, variables, types, strings, numbers, booleans, and comparison.

3
Syntax & Statements
Semicolons, comments, blocks, and the ASI trap.
syntax
→
4
Variables — let, const, var
Storing information. Why const is the default, when to use let.
variables
→
5
Data Types
The 7 primitives, typeof, and the null vs undefined trap.
types
→
6
Numbers & Math
One number type, NaN, Infinity, the Math object.
numbers
→
7
Strings
Template literals, immutability, the key string methods.
strings
→
8
Booleans & Comparison
=== vs ==, the falsy list, logical operators, ??, ?.
comparison
→
9
Type Coercion & Casting
Implicit coercion, Number(), String(), Boolean() — where bugs hide.
coercion
→
📦 Stage 3 — Working with Data 3 lessons ▾

Control flow to make decisions, arrays to hold lists, and objects to hold structured data.

10
Control Flow
if/else, switch, for, while, for...of vs for...in.
control-flow
→
11
Arrays
The workhorse — create, loop, map, filter, reduce, spread.
data-structures
→
12
Objects
Key-value pairs, destructuring, spread, JSON.
data-structures
→
🔧 Stage 4 — Functions & Real Programs 4 lessons ▾

Functions, scope, closures, user I/O, and error handling — writing programs that actually do things.

13
Functions
Declarations, expressions, arrow functions, first-class functions.
functions
→
14
Scope & Closures
Where variables live, the closure concept, the loop trap.
scope
→
15
User Input & Output
console.log, prompt/readline — two homes, explained honestly.
io
→
16
Error Handling
try/catch/finally, Error types, throw, reading error messages.
errors
→