javascript/react-17-to-18

Upgrade React 17 apps to React 18 with phased dependency and API migrations.

1|Updated Mar 14, 2026

Search Tags:#testing #react #upgrade #strict-mode #server-rendering #react-18 #rendering-api

Ready to run

npx skills add https://github.com/RussBrown00/agent-skills --skill javascript-react-17-to-18

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Please help me install this Agent Skill.
Skill: javascript/react-17-to-18
Source: https://github.com/RussBrown00/agent-skills/tree/main/javascript-react-17-to-18
Command: npx skills add https://github.com/RussBrown00/agent-skills --skill javascript-react-17-to-18

SYSTEM DOCUMENTATION & REQUIREMENTS

💡 This Skill includes references (resource) components.

What problem does it solve?

Upgrading a React 17 codebase to React 18 safely requires careful planning, phased execution, and validation to avoid breaking changes, performance regressions, or SSR incompatibilities.

Core Features & Use Cases

Provides a phased upgrade plan that covers dependencies, rendering API changes, automatic batching, Strict Mode adjustments, testing updates, and React 19 preparation.
Includes practical guidance and real-world pitfalls to audit multiple entrypoints, root rendering patterns, and module compatibility.
Useful for teams modernizing large React apps, especially those with SSR or custom wrappers, and for validating compatibility before production.

Quick Start

Audit your project and begin with Phase 1: Dependencies, then proceed phase-by-phase using the references as your guide.

Frequently Asked Questions about javascript/react-17-to-18

High-intent search queries and answers about installing and using this skill.

FAQPage Schema

How do I upgrade React 17 to 18 without breaking server-side rendering?▼

Upgrading React 17 to 18 requires a phased plan that validates server-side rendering compatibility after updating dependencies and migrating rendering APIs. You must audit SSR wrappers to avoid breaking changes during the transition.

How do I migrate createRoot to replace ReactDOM.render in React 18?▼

Migrating to React 18 involves updating the rendering API by replacing ReactDOM.render with createRoot across all project entrypoints. This phased migration enables automatic batching and must be validated before proceeding to Strict Mode adjustments.

Why does React 18 Strict Mode double-invoke effects and how do I fix the fallout?▼

React 18 Strict Mode double-invokes effects to surface non-idempotent side effects. Addressing Strict Mode fallout requires auditing your effect cleanup functions and dependency updates to ensure they run safely under the new automatic batching behavior.

What is the best way to handle multiple entrypoints when upgrading to React 18?▼

The best way to handle multiple entrypoints during a React 18 upgrade is a phased execution plan that audits each root rendering pattern individually. You update dependencies first, then migrate each entrypoint to createRoot before validating.

Does upgrading to React 18 prepare my codebase for React 19?▼

Upgrading to React 18 prepares your codebase for React 19 by addressing compatibility, migrating deprecated rendering APIs, and enabling automatic batching. The phased upgrade plan includes specific preparation steps for future React 19 migrations.

What should I check before starting a React 17 to 18 upgrade?▼

Before upgrading React 17 to 18, you should audit your project for multiple entrypoints, custom root rendering patterns, and server-side rendering considerations. This prerequisite validation ensures your module compatibility and dependencies are ready for phased updates.