Learn JavaScript: Code & Build

Coddykit

Contains adsIn-app purchases

About this app

Learn JavaScript step by step, from your first variable to the event loop, and run your code right on your phone. This JS tutorial pairs 59 short courses with a JS editor, a JavaScript console and daily practice, so you write code instead of only reading about it.

WHAT YOU'LL LEARN
200 lessons in 59 courses, levelled A1 to C1:
• Basics: values and types, variables and scope, control flow, arrays and objects, functions and this
• Everyday JavaScript: strings, numbers and dates, template literals, optional chaining, destructuring, rest/spread, array methods, JSON, error handling
• The browser: DOM selection and manipulation, events and event delegation, forms, the Fetch API, localStorage, IndexedDB, Canvas, WebSockets, Web Workers
• Asynchronous JS: callbacks, promises, microtasks, async/await and an event loop deep dive
• Advanced topics: closures and the module pattern, classes and prototypes, iterators and generators, Proxy and Reflect, regex, performance and memory, ES modules vs CommonJS, Node vs browser differences
The first course is free. Lessons mix short explanations with questions and small code tasks.

JS LAB: DAILY PRACTICE ON YOUR DEVICE
JS Lab runs JavaScript on the phone itself, so answers come back instantly.
• Console: type JavaScript and see the result right away
• Predict the output: a few new cards every day; the engine runs each snippet to show the real answer
• Bug hunt: fix broken programs against a table of test cases
• Kata of the week: one coding challenge a week, free for everyone
• Event loop: step through the call stack, microtasks and tasks one at a time
• Arena: rebuild a target page with the DOM
• Build: describe a small app and get working code, or start from a ready template
• Interview: five timed JavaScript interview questions
• Recall: a review deck built from your own mistakes

JS EDITOR AND CODE RUNNER
• Write and run JS code in the built-in JS editor
• AI Tools in the editor review your program and suggest a fix you can apply
• Save your programs and open them again later

20 GUIDED PROJECTS
Build real programs one step at a time, each step checked when you run it: Order Totals, Word Frequency Counter, Async Data Pipeline, Mini Event Bus, Log Line Parser, File Tree Walker, Sequence Generators and more. The first project is free.

60 CODING MISSIONS
Short coding exercises in three levels, from Hello World and template literals to FizzBuzz, closures, Merge Sort, Quicksort and BFS/DFS on a graph. The first two missions are free.

AI MENTOR
Stuck on a concept or an error? Ask the AI Mentor and get an explanation in plain language. Free users get a few AI questions every day; Pro removes the daily limit.

MORE WAYS TO PRACTISE
• Quizzes with 50 questions, flashcards and a JS cheat sheet
• 50 JavaScript interview questions with answers
• Code examples you can open in the editor
• World Coding Challenge: three global rounds every day; solve them in JavaScript or another language
• Streaks, XP and daily reminders at the time you choose
• The app is available in 22 languages

WHO IT'S FOR
• Complete beginners who have never programmed before
• Students who want extra JS practice next to their classes
• Developers preparing for a JavaScript interview
• Anyone who wants to understand how JavaScript really works

FREE AND PRO
Free: the first course, the first guided project, two coding missions, JS Lab daily practice and a daily AI Mentor allowance. The free version shows ads.
Pro: every course, project and mission, unlimited AI Mentor, the certificate exam and no ads.

Download Learn JavaScript: Code & Build and write your first line of JavaScript today.