javascript/react-17-to-18

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.

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.

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.

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.

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.

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.