🟨 JavaScript Study Book
An intermediate, chapter-by-chapter course through the MDN JavaScript Guide and its intermediate and advanced topics. It's built around everything ES6 changed and everything added since, for developers who can already write basic JavaScript (or Java) and want to understand it properly.
How to use this book
- Read in order. The 16 chapters follow MDN's Guide, grouped into six parts. Each chapter uses only ideas from earlier ones, or says where an idea is explained.
- Watch the badges. ES2015 marks ES6 features; ES2020-style badges show when later features arrived. Chapter 1 has the full timeline and an "ES6 at a glance" table.
- Type the examples. Every example was run on Node 26 and its output checked.
>blocks are REPL sessions; file blocks are ES modules. Use the Copy button. - Do the exercises. Each chapter has 10+ exercises marked 🟢 easy, 🟡 medium or 🔴 hard, with hidden solutions. Playground exercises grow towards the Chapter 16 project.
- Test yourself. The Final Assessment draws 50 random questions from a pool of 1000, and scores you per chapter.
- Practise beyond the book. The 🧩 Problem Set has 100 language-neutral problems (easy, medium, hard and OOP) with exact tests — a great way to make JavaScript stick.
💡 Rusty on pre-2015 JavaScript, or on Node tooling? Appendix A: ES5 to ES6+ Refresher maps old idioms to modern ones, and Appendix B: Node.js, npm & DevTools covers running, testing and debugging. First time here? Start with Using the Playground.
🟩 Next step: once you're comfortable with the language, the Node.js Study Book takes you from scripts to a tested HTTP API: modules, npm, the event loop, streams, servers, workers and testing.
📝 Setup: install Node 26 LTS and check it with node --version, then clone the practice project, coder-hop/js-book-playground, with git clone https://github.com/coder-hop/js-book-playground.git playground. Node 24 runs nearly everything, except Temporal and a few ES2025/2026 additions.
Keep practising
🧩 100 Practice Problems
25 easy, 25 medium, 25 hard and 25 object-oriented problems with exact test cases. Start the easy set after Chapter 8 (Arrays) and the OOP set after Chapter 11 (Classes & the Prototype Chain). Check with node runner/run-tests.mjs E01 -- node e01.mjs.
🛠️ How to Solve & Test
Reading stdin and printing stdout in JavaScript, the OOP command-loop template, and the test runner.