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react18-lifecycle-patterns

Provides exact before/after migration patterns for the three unsafe class component lifecycle methods - componentWillMount, componentWillReceiveProps, and componentWillUpdate - targeting React 18.3.1. Use this skill whenever a class component needs its lifecycle methods migrated, when deciding between getDerivedStateFromProps vs componentDidUpdate, when adding getSnapshotBeforeUpdate, or when fixing React 18 UNSAFE_ lifecycle warnings. Always use this skill before writing any lifecycle migration code - do not guess the pattern from memory, the decision trees here prevent the most common migration mistakes.

skills/react18-lifecycle-patterns/SKILL.md

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# React 18 Lifecycle Patterns

Reference for migrating the three unsafe class component lifecycle methods to React 18.3.1 compliant patterns.

## Quick Decision Guide

Before migrating any lifecycle method, identify the **semantic category** of what the method does. Wrong category = wrong migration. The table below routes you to the correct reference file.

### componentWillMount - what does it do?

| What it does | Correct migration | Reference |
|---|---|---|
| Sets initial state (`this.setState(...)`) | Move to `constructor` | [→ componentWillMount.md](references/componentWillMount.md#case-a) |
| Runs a side effect (fetch, subscription, DOM) | Move to `componentDidMount` | [→ componentWillMount.md](references/componentWillMount.md#case-b) |