javascript 54 lines · 8 steps

Memoizing a filtered list in React

A search-and-sort product list that recomputes its visible items only when the inputs that matter actually change.

Explained by highlit

React Intermediate memoization derived-state filtering sorting controlled-inputs

1import { useMemo, useState } from 'react';
2 
3function ProductList({ products }) {
const [query, setQuery] = useState('');
const [minRating, setMinRating] = useState(0);
const [sortBy, setSortBy] = useState('relevance');
7 
const visibleProducts = useMemo(() => {
  const term = query.trim().toLowerCase();
10 
  const filtered = products.filter((product) => {
    if (product.rating < minRating) return false;
    if (!term) return true;
    return (
      product.name.toLowerCase().includes(term) ||
      product.tags.some((tag) => tag.toLowerCase().includes(term))
    );
  });
19 
  if (sortBy === 'price') {
    filtered.sort((a, b) => a.price - b.price);
  } else if (sortBy === 'rating') {
    filtered.sort((a, b) => b.rating - a.rating);
  }
25 
  return filtered;
}, [products, query, minRating, sortBy]);
28 
return (
  <div className="product-list">
    <input
      type="search"
      value={query}
      placeholder="Search products"
      onChange={(e) => setQuery(e.target.value)}
    />
    <select value={sortBy} onChange={(e) => setSortBy(e.target.value)}>
      <option value="relevance">Relevance</option>
      <option value="price">Price</option>
      <option value="rating">Rating</option>
    </select>
    <p>{visibleProducts.length} results</p>
    <ul>
      {visibleProducts.map((product) => (
        <li key={product.id}>
          {product.name} — ${product.price.toFixed(2)}
        </li>
      ))}
    </ul>
  </div>
);
52}
53 
54export default ProductList;

01 / 01

STEP 01

Walkthrough

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Three takeaways

1Derive displayed data from state inside render rather than storing a second copy you have to keep in sync.
2Wrap expensive list transforms in useMemo with an honest dependency array so they rerun only when an input changes.
3Controlled inputs feed state, state feeds the memo, and the memo feeds the UI in one predictable flow.

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