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- Adds React 18 and 19 migration orchestration plugins - Introduces comprehensive upgrade toolkits for migrating legacy React 16/17 and 18 codebases to React 18.3.1 and 19, respectively. Each plugin bundles specialized agents and skills for exhaustive audit, dependency management, class/component API migration, test suite transformation, and batching regression fixes. - The React 18 toolkit targets class-component-heavy apps, ensures safe lifecycle and context transitions, resolves dependency blockers, and fully automates test migrations including Enzyme removal. The React 19 toolkit addresses breaking changes such as removal of legacy APIs, defaultProps on function components, and forwardRef, while enforcing a gated, memory-resumable migration pipeline. - Both plugins update documentation, plugin registries, and skill references to support reliable, repeatable enterprise-scale React migrations.
64 lines
3.6 KiB
Markdown
64 lines
3.6 KiB
Markdown
---
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name: react18-lifecycle-patterns
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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.'
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---
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# React 18 Lifecycle Patterns
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Reference for migrating the three unsafe class component lifecycle methods to React 18.3.1 compliant patterns.
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## Quick Decision Guide
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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.
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### componentWillMount - what does it do?
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| What it does | Correct migration | Reference |
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| Sets initial state (`this.setState(...)`) | Move to `constructor` | [→ componentWillMount.md](references/componentWillMount.md#case-a) |
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| Runs a side effect (fetch, subscription, DOM) | Move to `componentDidMount` | [→ componentWillMount.md](references/componentWillMount.md#case-b) |
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| Derives initial state from props | Move to `constructor` with props | [→ componentWillMount.md](references/componentWillMount.md#case-c) |
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### componentWillReceiveProps - what does it do?
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| What it does | Correct migration | Reference |
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|---|---|---|
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| Async side effect triggered by prop change (fetch, cancel) | `componentDidUpdate` | [→ componentWillReceiveProps.md](references/componentWillReceiveProps.md#case-a) |
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| Pure state derivation from new props (no side effects) | `getDerivedStateFromProps` | [→ componentWillReceiveProps.md](references/componentWillReceiveProps.md#case-b) |
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### componentWillUpdate - what does it do?
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| What it does | Correct migration | Reference |
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| Reads the DOM before update (scroll, size, position) | `getSnapshotBeforeUpdate` | [→ componentWillUpdate.md](references/componentWillUpdate.md#case-a) |
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| Cancels requests / runs effects before update | `componentDidUpdate` with prev comparison | [→ componentWillUpdate.md](references/componentWillUpdate.md#case-b) |
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---
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## The UNSAFE_ Prefix Rule
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**Never use `UNSAFE_componentWillMount`, `UNSAFE_componentWillReceiveProps`, or `UNSAFE_componentWillUpdate` as a permanent fix.**
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Prefixing suppresses the React 18.3.1 warning but does NOT:
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- Fix concurrent mode safety issues
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- Prepare the codebase for React 19 (where these are removed, with or without the prefix)
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- Fix the underlying semantic problem the migration is meant to address
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The UNSAFE_ prefix is only appropriate as a temporary hold while scheduling the real migration sprint. Mark any UNSAFE_ prefix additions with:
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```jsx
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// TODO: React 19 will remove this. Migrate before React 19 upgrade.
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// UNSAFE_ prefix added temporarily - replace with componentDidMount / getDerivedStateFromProps / etc.
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```
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---
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## Reference Files
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Read the full reference file for the lifecycle method you are migrating:
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- **`references/componentWillMount.md`** - 3 cases with full before/after code
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- **`references/componentWillReceiveProps.md`** - getDerivedStateFromProps trap warnings, full examples
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- **`references/componentWillUpdate.md`** - getSnapshotBeforeUpdate + componentDidUpdate pairing
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Read the relevant file before writing any migration code.
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