The Lab

Learn by fixing things that are really broken.

No long videos, no quizzes on words you haven't met. Each task is a small bug in a live app. You'll fix it in a minute or two, and you'll know exactly why it worked.

Modules

Module 1 · 7 sessions

Build a tiny To-Do app

How JavaScript really runs

Seven small bugs in a live To-Do app. Each one teaches an idea interviewers love to ask about.

1.1Values & memory
1.2The event loop
1.3Generics
1.4Conditional & mapped types
1.5Narrowing & tagged unions
1.6Promises & async
1.7Concurrency control

Start module About 20 minutes. Your progress stays in this browser.

More modules are on the way.

How each task works

01
Fix a real bug
A tiny To-Do app misbehaves. Change one chip of code and watch it recover.
02
See inside
A short picture shows what really happened, in plain words first.
03
Practise the interview
The same idea, asked the way interviewers ask it, Fresher to Senior.