How to access impure values during render (initially labeled as compiler bug) about react

[josephsavona]

Thanks for posting. One of the key rules of React is that components and hooks must be pure. That is, they should be pure functions of their props, state, and context. Functions such as Math.random() and new Date() are impure, and cause render results to change even though props, state, and context haven't.

React Compiler builds on this rule to optimize code. In this case, it's fine to access Math.random() or new Date() in an event handler or effect. But to give the best advice it would help to understand why you need to access these in render.

[jithyan]

Yes you're correct, the logic would be more accurate if re-written to calculate the timestamp on retrieval rather than on render. I assumed the compiler would have bailed on memoization if I violated a rule, but that was a mistake on my part.