Caching expensive calculations

caching-expensible-calculation.ts

function TodoList({ todos, filter }) {
  const [newTodo, setNewTodo] = useState('');
  // ✅ This is fine if getFilteredTodos() is not slow.
  const visibleTodos = getFilteredTodos(todos, filter);
  // ...
}

import { useMemo, useState } from 'react';

function TodoList({ todos, filter }) {
  const [newTodo, setNewTodo] = useState('');
  const visibleTodos = useMemo(() => {
    // ✅ Does not re-run unless todos or filter change
    return getFilteredTodos(todos, filter);
  }, [todos, filter]);
  // ...
}

import { useMemo, useState } from 'react';

function TodoList({ todos, filter }) {
  const [newTodo, setNewTodo] = useState('');
  // ✅ Does not re-run getFilteredTodos() unless todos or filter change
  const visibleTodos = useMemo(() => getFilteredTodos(todos, filter), [todos, filter]);
  // ...
}