What are truthy and falsy values?
PICTURE THIS: ARRAY IN MEMORY
Index starts at 0. Scan once for max — O(n).
Simple meaning
Falsy values are false, 0, empty string, null, undefined, and NaN.
WHY — JavaScript instead of guessing?
Why interviewers care about JavaScript:
who only read docs from people who shipped.
and tied to Frontend work.
Name the idea, why it exists, then one short example.
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:
- 1Falsy values are false,
0, empty string, null, undefined, and NaN.
- 2Everything else is truthy,
including empty arrays and objects.
- 3I am careful with
if (value) when 0 or empty string is valid user input.
- 4Give an example
One tiny concrete case you can say aloud.
- 5Common mistake
What juniors usually get wrong.
- 6Close
When you pick this over the alternative.
EXAMPLE — See it in action
Here's a short line you can speak, broken into clear beats:
Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.
Key takeaway
Falsy values are false, 0, empty string, null, undefined, and NaN. Everything else is truthy, including empty arrays and objects.