See how JavaScript actually runs.
Predict the output. Watch every step. Finally understand why.
No signup. No setup. ~8 minutes per case.
Predict
Commit to an output before you see anything. That is where learning starts.
Watch
Step through the engine: Call Stack, Web APIs, both queues, the console.
Understand
A few rules explain the whole thing — right after you watched them work.
Experiment
One line changes. Predict again. Does your model survive?
The series
Real snippets developers get wrong — with the exact misconception named when you do.
How Promises Run
Promise vs setTimeout
The classic interview question. setTimeout is registered BEFORE the promise — so why does the promise callback run first? Watch the two queues to find out.
How the Event Loop Runs
setTimeout(fn, 0)
Your first look inside the JavaScript runtime: watch synchronous code claim the Call Stack while a "0ms" timer waits its turn in the Task Queue.
How await Runs
async / await
async/await is syntactic sugar over promises. See the exact moment main() suspends, where its continuation waits, and why the global script keeps running.