StrictMode-safe Effect Setup and Cleanup

Challenge summary

Build a React effect with symmetrical setup and cleanup through StrictMode checks, dependency changes, rerenders, and unmounting. Treat the effect as a reversible synchronization process with clear resource ownership.

What you'll practice

• Pair every effect setup with cleanup for the same resource.
• Declare every reactive dependency used by the effect.
• Remain correct through the StrictMode setup, cleanup, and setup sequence.
• Replace the resource safely when its room dependency changes.
• Leave no active resource after the component unmounts.

What Premium unlocks

Premium unlocks the runnable workspace, behavioral checks, implementation walkthrough, and edge-case discussion.