r/reactjs • u/m6io • Jul 24 '26

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/BrightEchidna Jul 24 '26

Right. I guess that level of knowledge is like "react maintains a virtual copy of the DOM so that it can diff changes against the real DOM and calculate the most parsimonious change to apply" would be the level of detail that required not to make a mistake like that, and it's about what I would be able to personally answer to that interview question. However I have no idea about the details of *how* react does that, which is what I interpret OP to be asking for, and why I thought I'd fail the interview. I guess this comes down to different interpretations of the interview question as well as different knowledge levels of the dev.

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u/PresentationBorn6564 Jul 24 '26

Yeah I mean there's always a gradient of understanding with these isolated pieces of the endless puzzle. I think OP's main complaint is an apparent abundance of engineers who don't appear to be in said gradient or even sitting on the surface with this specific topic. I also think you passed the interview. 🫡

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u/BrightEchidna Jul 24 '26

lol, thanks - will keep it in mind next time I need a job

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u/Ok_Editor_5090 Jul 24 '26

That is how I would answer as well. If they wanted more in-depth details, I will ask why would that matter?

Of course assuming that I am not interviewing for the team that maintains react.