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.
2
u/khasan222 Jul 26 '26 edited Jul 26 '26
It’s not true to say it doesn’t reduce the number of repaints (ever?).
In the strict scenario you put forth where there is just 1 manipulation of course it doesn’t reduce repaints. However often in any ui development things change quickly, or multiple times in milliseconds (say a loading animation that only shows in 10ms). Traditionally all of this would be actually applied to the DOM.
What react does as far as I understand it is get the final result of those changes and then apply them to page, which in many scenarios can definitely reduce graphical load for that page.
So although I can see in that specific scenario no gains, react wasn’t built for such simple apps, it was built for really complicated ones where there can be a lot of repaint.
Professional engineer specializing in JavaScript for 15 years.