What is a hydration mismatch?
PICTURE THIS: DOM IS A TREE
Simple meaning
The HTML from the server does not equal what React renders on the client for the first pass.
WHY — Next.js instead of guessing?
Why interviewers care about Next.js:
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:
- 1The HTML from the
server does not equal what React renders on the client for the first pass.
- 2Causes include Date.now, random
ids, invalid HTML nesting, and browser-only APIs in render.
- 3The user may see
a flash and event handlers attach to the wrong nodes.
- 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
The HTML from the server does not equal what React renders on the client for the first pass. Causes include Date.now, random ids, invalid HTML nesting, and browser-only APIs in render.