Explore
Explore courses, bite-sized lessons, tutorials, and assessments.
Advanced JavaScript
The object model, this and binding, classes, the microtask queue, generators, modules and the patterns interviews actually ask about.
JavaScript for Beginners
Learn JavaScript from the first line of code. Variables, types, operators, decisions, loops, functions, strings, arrays and objects, each one explained before it is used.
Intermediate JavaScript
Execution contexts, hoisting, scope chains, closures and the event loop. How JavaScript actually runs your code, and why the quirks stop being quirks once you can see the mechanism.
A URL Reaches Your Server. What Happens Next?
Build one small API from route to response, then see when a database and cache join the request.
How LLMs Work: Build One Small Enough to Understand
Follow a tiny next-token predictor until the logic behind modern language models becomes clear.
How the Web Works
Follow one page visit from the address bar to the pixels on your screen.
SQL Fundamentals
Twenty-five questions on reading SQL and predicting what it returns: NULLs, joins, grouping, window functions, and the order a query actually runs in.
Basic System Design
Thirty questions on what breaks when a system grows: isolation levels, sharding keys, cache invalidation, queues, and the failure each one introduces.
JavaScript Fundamentals
Twenty-five questions on how JavaScript actually runs: hoisting, the temporal dead zone, closures, the event loop, and the parts that surprise people.