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UI Component Not Rendering After State Update

A UI component successfully updates its state but the changes don't appear on screen. The developer confirms the state changed (via console logging) but the component remains visually unchanged. This typically affects forms, lists, and modal dialogs.

The component structure and lifecycle are correct, but something prevents the rendering system from detecting the state change as significant.

Error Messages You Might See

State changed but component didn't update No error in console but UI is stale List items duplicated or in wrong order after update
State changed but component didn't updateNo error in console but UI is staleList items duplicated or in wrong order after update

Common Causes

  1. State mutation instead of immutable state update (mutating object directly)
  2. Using direct array operations (push, splice) instead of immutable alternatives (concat, slice)
  3. Key prop missing or incorrect in list rendering causing elements to be reused
  4. Setter function called but returns same reference due to incorrect comparison
  5. Parent component not re-rendering when child receives new props

How to Fix It

Never mutate state directly. Use spread operator or Object.assign() for objects, array methods like concat/slice for arrays. Add explicit keys to list items using unique identifiers, never array index. Use immutable patterns: setState(prev => ({...prev, field: value})). Verify dev tools show state changing. Add console.log in render to confirm render called.

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Frequently Asked Questions

How to fix state mutations?

Never do: state.field = value. Instead: setState({...state, field: value}). For arrays: [...state, newItem] not state.push(newItem).

Why are list keys important?

Keys help the framework identify which items changed, were added, or removed. Always use stable, unique identifiers (id), never array index.

How to debug re-render issues?

Add console.log at component top. If it logs when state changes, component renders but view isn't updating (mutation issue). If it doesn't log, state isn't triggering re-render.

Related Claude Code Issues

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