Use Strict teaches JavaScript (JS) through short coding lessons built around code examples, from the basics to modern ES6+ features. Read a snippet, predict what it prints, fill in the missing piece or find the line that breaks it, and then read a clear explanation of why JavaScript behaves the way it does.

Every exercise is solved with taps, so there is no typing code on a phone keyboard, and a lesson fits into a commute or a coffee break.

HOW YOU LEARN
• Each lesson opens with short theory cards and examples
• Predict the output of a snippet or put the printed lines in order
• Fill in the blanks, match pairs, answer true or false and quizzes
• Find the bug and choose the right fix
• After every answer, a detailed explanation, including why the other options are wrong

ANSWERS YOU CAN TRUST
Every snippet that can run has been run in Node.js, so the right answer really is right.

27 MODULES, 108 LESSONS, 670 EXERCISES
Values and types, coercion, scope, functions, closures, this, objects, prototypes and classes, arrays, destructuring, strings and numbers, dates and Intl, errors, iterators and generators, Map and Set, JSON, promises, async and await, the event loop, cancellation, modules, regular expressions, immutability, Proxy and Reflect, performance, security and clean code. 490 theory cards and a searchable reference cover the theory.

The recommended path leads from the basics to advanced topics, and every module is open from the start, so you can jump straight to what you need.

FOR EVERY LEVEL
Exercises go from difficulty 1 to 5. Beginners learn programming basics without overload, and web and frontend developers who already write JavaScript close the gaps and prepare for job interviews.

REMEMBER WHAT YOU LEARN
• Spaced repetition brings back the exercises you got wrong at the right time
• A mistakes session, bookmarks and a searchable theory reference
• Chapter exams to check yourself
• Interview mode: hard questions with a soft timer
• Statistics, an activity calendar, a calm day streak and achievements

RESPECTS YOU
• No account, no ads, no tracking
• Works fully offline
• Your progress stays on your device; export it to a file whenever you want
• Optional reminders at the time and on the days you choose
• Light and dark themes, several code highlighting themes, adjustable code font size
• English and Russian