react18-batching-patterns

by github

Provides exact patterns for diagnosing and fixing automatic batching regressions in React 18 class components. Use this skill whenever a class component has… npx skills add https://github.com/github/awesome-copilot --skill react18-batching-patterns Download ZIPGitHub36.2k

React 18 Automatic Batching Patterns

Reference for diagnosing and fixing the most dangerous silent breaking change in React 18 for class-component codebases.

The Core Change

Location of setState React 17 React 18 React event handler Batched Batched (same) setTimeout Immediate re-render Batched Promise .then() / .catch() Immediate re-render Batched async/await Immediate re-render Batched Native addEventListener callback Immediate re-render Batched

Batched means: all setState calls within that execution context flush together in a single re-render at the end. No intermediate renders occur.

Quick Diagnosis

Read every async class method. Ask: does any code after an await read this.state to make a decision?

Code reads this.state after await?
 YES → Category A (silent state-read bug)
 NO, but intermediate render must be visible to user?
 YES → Category C (flushSync needed)
 NO → Category B (refactor, no flushSync)

For the full pattern for each category, read:

• references/batching-categories.md - Category A, B, C with full before/after code

• references/flushSync-guide.md - when to use flushSync, when NOT to, import syntax

The flushSync Rule

Use flushSync sparingly. It forces a synchronous re-render, bypassing React 18's concurrent scheduler. Overusing it negates the performance benefits of React 18.

Only use flushSync when:

• The user must see an intermediate UI state before an async operation begins

• A spinner/loading state must render before a fetch starts

• Sequential UI steps have distinct visible states (progress wizard, multi-step flow)

In most cases, the fix is a refactor - restructuring the code to not read this.state after await. Read references/batching-categories.md for the correct approach per category.