> Do they understand how useEffect actually works?
What do you mean? If you're asking if they can and do use useEffect for its intended purpose regularly and don't run into edge cases any more often than with any other coding pattern, then yeah, they understand how useEffect actually works. If you're asking if they have a deep technical understanding of how hooks are implemented in the React library and every potential "gotcha" they might ever run into, then sure, probably not, but the same goes for every basic pattern used in any programming language.
What do you mean? If you're asking if they can and do use useEffect for its intended purpose regularly and don't run into edge cases any more often than with any other coding pattern, then yeah, they understand how useEffect actually works. If you're asking if they have a deep technical understanding of how hooks are implemented in the React library and every potential "gotcha" they might ever run into, then sure, probably not, but the same goes for every basic pattern used in any programming language.