The examples
In curriculum order — each one asks for your prediction first, then animates exactly why. Warm-ups build the model, core examples are the interview classics, advanced ones break the loop on purpose.
- Fig. 1warm-up
One thing at a time
No async at all — how the stack really runs your code.
7 steps · predict first →
- Fig. 2warm-up
setTimeout(0), alone
Zero milliseconds does not mean now.
7 steps · predict first →
- Fig. 3warm-up
A promise, alone
Even an already-resolved promise waits its turn.
6 steps · predict first →
- Fig. 4core
Promise vs setTimeout
The classic showdown — and the classic interview question.
9 steps · predict first →
- Fig. 5core
.then after .then
Each link in a .then chain is its own microtask.
7 steps · predict first →
- Fig. 6core
async/await, unmasked
Watch a function leave the stack mid-body.
7 steps · predict first →
- Fig. 7advanced
Starving the loop
VIPs forever — the timer never eats.
8 steps · predict first →
- Fig. 8advanced
Blocking the loop
One hot loop freezes the whole page.
6 steps · predict first →