Moderate JavaScript Question 130 of 229

What memory leak might you cause with addEventListener?

Frontend Master · Speak this in 60–90 seconds · Faridabad & Delhi NCR

PICTURE THIS: A CLOSURE

Outer fnCreates count = 0

Inner fnStill sees count

LaterIncrement works

Simple meaning

If I add a window resize listener in useEffect and forget the cleanup, the handler keeps the component closure alive after unmount.

WHY — JavaScript instead of guessing?

Why interviewers care about JavaScript:

JavaScript questions separate people

who only read docs from people who shipped.

Keep it short, concrete,

and tied to Frontend work.

Stay structured

Name the idea, why it exists, then one short example.

Close cleanly

End with when you use it and one common pitfall.

STEPS — What happens step by step?

Before you speak the answer, walk the interviewer through these steps:

1
If I add a
window resize listener in useEffect and forget the cleanup, the handler keeps the component closure alive after unmount.
2
Why it exists
The same happens with setInterval.
3
I always return a
function that removes the listener or clears the timer.
4
Give an example
One tiny concrete case you can say aloud.
5
Common mistake
What juniors usually get wrong.
6
Close
When you pick this over the alternative.

EXAMPLE — See it in action

Here's a short line you can speak, broken into clear beats:

Say this line

“The same happens with setInterval.”

Break into beats

ThesamehappenswithsetInterval

Speaking order

298740833747163290

Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.

Key takeaway

If I add a window resize listener in useEffect and forget the cleanup, the handler keeps the component closure alive after unmount. The same happens with setInterval.