React 17

About React 17

React 17 was a 'stepping stone' release with no new developer-facing features. Its purpose was to make gradual React upgrades possible by allowing multiple React versions to coexist on the same page.

Key Changes in React 17

• ●Gradual upgrades: multiple React versions can coexist on a single page
• ●Event delegation changed from document to root DOM container
• ●New JSX transform (no more import React needed in every file)
• ●Consistent error handling with native browser stack traces
• ●Effect cleanup timing aligned with screen paint

Breaking Changes

• ▲Event delegation changed from document-level to root-level (may affect event handling in mixed React/non-React apps)
• ▲Event pooling removed (SyntheticEvent reuse behavior changed)
• ▲forwardRef and memo components now behave consistently

React 17 is currently under active support, released on October 20, 2020. It receives regular bug fixes, security patches, and may still get minor feature additions. The latest patch release is 17.0.2 (March 22, 2021).

Migration Notes

React 17 was specifically designed to enable gradual migration. You can upgrade parts of your app to React 18 while keeping others on React 17. The new JSX transform is optional but recommended for cleaner imports.

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Frequently Asked Questions

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