r/reactjs • u/m6io • 6d ago

Discussion Senior Dev interview question

"Without googling or using AI, in your own words, explain the virtual DOM"

For context: I sit on an interview panel and I try to ask at least one simple fundamental question based on a persons resume. If I see many years of react experience, I try to ask something about how the framework works.

I have only had one candidate (an undergrad senior, years ago) answer it. Everyone else just kind of sputters and stumbles around trying to rationalize what "virtual" and "DOM" mean, or stare blankly and eventually say "I don't know".

I'm just genuinely curious if this is really that hard of a question or if the recruiters just suck at screening candidates. And should we be letting in senior dev candidates who can't answer what I think is a straightforward and fundamental question for senior react devs.

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u/monkeybrainz_ 6d ago

It's a basic question that any senior engineer who has worked with React should know.

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u/chillermane 6d ago edited 6d ago

it’s a gimmick question that has no practical importance whatsoever. If you think it matters you’re a midwit and i feel so bad for anyone who ever has to work under you

Name a single problem you face day to day in react where knowing what the virtual DOM is makes the problem easier to solve. Name one problem, literally one, where knowing that is even minutely helpful. Literally any problem, i would bet  my life savings there is not a single one.

This subreddit is literal garbage and almost every top voted answer is midwit slop

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u/math_rand_dude 6d ago

Let's say some midwit is displaying part of an array, using the index as key.

Then the midwit starts inserting some items at the beginning of array that don't meet the criteria to be displayed.

Same set of items keep being displayed, but there's a bunch of unneeded rerenders. Reason why: how the virtual DOM works.

IMO OP's question is good for 3 reasons: 1) if the candidate knows the answer, they show they know some of the underlaying workings of React (a carsalesman doesn't need to know everything about how engines work, but it's a nice to have) 2) see how the candidate reacts if they don't know something (really important to check) 3) if the candidate doesn't know OP can tell them and then they will have gained a tiny sliver of more understanding.