Learn JavaScript like a backend engineer.JavaScript → TypeScript → production Node.
Three courses that take you from closures and the event loop to production TypeScript APIs and shipped Node services. Every exercise is graded by a real Node test suite — the async model every backend job screens for — so “it works” is never a vibe. No videos, ever.
// mapLimit runs async tasks with at most `limit` in flight at once.
// The grader runs a real node --test suite — ordering and the
// concurrency ceiling are asserted, not eyeballed.
async function mapLimit(items, limit, fn) {
const results = new Array(items.length);
let next = 0;
async function worker() {
while (next < items.length) {
const i = next++;
results[i] = await fn(items[i], i);
}
}
await Promise.all(Array.from({ length: limit }, worker));
return results;
}JavaScript & Async Foundations
Modern JavaScript for people who want backend jobs — values, closures, classes, Promises and the event loop: the async model every backend interview screens for.
TypeScript & Node Backends
Production-grade TypeScript REST APIs on Node — types, HTTP servers, auth, and persistence, capped by capstones like a link shortener and the Bookshelf REST API.
Production Node: Testing, Shipping & Performance
The production tier — inverted mutation grading, 12-factor config, Docker analysis, performance fixes, and the Ledger multi-tenant invoicing API capstone.
The tests decide, not vibes
Your code runs against real Node and TypeScript test suites. Pass/fail is deterministic — the AI never grades you.
It adapts to you
Struggle on a concept and the game diagnoses why and builds targeted practice. Already know Promises? It moves you up instead of making you sit through it.
Ship real backends
Capstones like an auth service and a multi-tenant invoicing API, with a senior-engineer code review — the answer to tutorial hell. Ship a portfolio, not just streaks.
Your first passing Node test is minutes away.
Start the JavaScript track — freeFree tier is genuinely free — every banked exercise is playable. We gate AI help and fresh generation, never the content.