AgentSkillsCN

react18-lifecycle-patterns

提供精确的前后迁移模式，针对 React 18.3.1 的三个不安全的类组件生命周期方法——componentWillMount、componentWillReceiveProps 和 componentWillUpdate。当类组件需要迁移其生命周期方法、在 getDerivedStateFromProps 与 componentDidUpdate 之间做决定、添加 getSnapshotBeforeUpdate，或修复 React 18 UNSAFE_ 生命周期警告时使用这项技能。编写任何生命周期迁移代码前务必使用这项技能——不要凭记忆猜测模式，这里的决策树可防止最常见的迁移错误。

SKILL.md
--- frontmatter
name: react18-lifecycle-patterns
description: '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.'

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 doesCorrect migrationReference
Sets initial state (this.setState(...))Move to constructor→ componentWillMount.md
Runs a side effect (fetch, subscription, DOM)Move to componentDidMount→ componentWillMount.md
Derives initial state from propsMove to constructor with props→ componentWillMount.md

componentWillReceiveProps - what does it do?

What it doesCorrect migrationReference
Async side effect triggered by prop change (fetch, cancel)componentDidUpdate→ componentWillReceiveProps.md
Pure state derivation from new props (no side effects)getDerivedStateFromProps→ componentWillReceiveProps.md

componentWillUpdate - what does it do?

What it doesCorrect migrationReference
Reads the DOM before update (scroll, size, position)getSnapshotBeforeUpdate→ componentWillUpdate.md
Cancels requests / runs effects before updatecomponentDidUpdate with prev comparison→ componentWillUpdate.md

The UNSAFE_ Prefix Rule

Never use UNSAFE_componentWillMount, UNSAFE_componentWillReceiveProps, or UNSAFE_componentWillUpdate as a permanent fix.

Prefixing suppresses the React 18.3.1 warning but does NOT:

  • •Fix concurrent mode safety issues
  • •Prepare the codebase for React 19 (where these are removed, with or without the prefix)
  • •Fix the underlying semantic problem the migration is meant to address

The UNSAFE_ prefix is only appropriate as a temporary hold while scheduling the real migration sprint. Mark any UNSAFE_ prefix additions with:

jsx
// TODO: React 19 will remove this. Migrate before React 19 upgrade.
// UNSAFE_ prefix added temporarily - replace with componentDidMount / getDerivedStateFromProps / etc.

Reference Files

Read the full reference file for the lifecycle method you are migrating:

  • •references/componentWillMount.md - 3 cases with full before/after code
  • •references/componentWillReceiveProps.md - getDerivedStateFromProps trap warnings, full examples
  • •references/componentWillUpdate.md - getSnapshotBeforeUpdate + componentDidUpdate pairing

Read the relevant file before writing any migration code.