React18 Lifecycle Patterns

If you're still maintaining React class components and hitting UNSAFE_ warnings in 18.3.1, this gives you exact migration patterns for the three deprecated lifecycle methods. The decision tables are the real value here: they route you to the right replacement based on what the code actually does, not just which method name you're replacing. componentWillReceiveProps doing a fetch goes to componentDidUpdate, pure state derivation goes to getDerivedStateFromProps, and the guide is explicit about which is which. Saves you from the classic mistake of reaching for getDerivedStateFromProps when you actually need componentDidUpdate with a prev prop comparison. The references include full before and after code blocks for each case.