setState is not a function
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Unique “key” Prop Required for List Items
Warning: Each child in a list should have a unique "key" prop
Introduction:
The warning “Each child in a list should have a unique ‘key’ prop” in React signals that each element in a list must have a unique identifier assigned to its key prop. This is essential for React to efficiently update and manage the list during changes like additions or deletions. Without unique keys, React may struggle to track changes, resulting in performance issues and unexpected behavior. Let’s look at how to implement keys correctly in lists.
Understanding the Importance of Key Props in React Lists
The Problem:
When rendering a list of elements, React requires each element to have a unique key to help with efficient updates:
const items = [{ name: ‘Item1’ }, { name: ‘Item2’ }];
return items.map(item => <div>{item.name}</div>); // Warning: No key provided
The Solution:
Ensure each child element in the list has a unique key prop:
return items.map((item, index) => (
<div key={index}>{item.name}</div>
));
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