QReact · Interview preparation
When is useCallback useful in React?
useCallback preserves a function reference between renders when its dependencies stay the same.
The idea to remember.
useCallback preserves a function reference between renders when its dependencies stay the same. It can help when passing callbacks to memoized children or maintaining stable dependencies, but adds complexity.
01Learn by doing
From first example to real project.
Start with the smallest working idea, examine a more detailed example, then look at a real application pattern. Adapt dependencies, error handling and data models to your project.
Basic: understand a render
01 / BEGINNERA render calculates UI; it does not always change the DOM.
function Greeting({ name }) {
console.count('Greeting rendered');
return <h2>Hello, {name}</h2>;
}Intermediate: memoize derived work
02 / INTERMEDIATEMemoize an expensive derived value when profiling justifies it.
const visibleRows = React.useMemo(
() => rows.filter(row => row.label.includes(query)),
[rows, query]
);Real scenario: stabilize props
03 / REAL SCENARIOOnly optimize a frequently updated dashboard after measuring.
const Chart = React.memo(function Chart({ data }) {
return <Graph data={data} />;
});
function Dashboard({ records, filter }) {
const data = React.useMemo(() => aggregate(records, filter), [records, filter]);
return <Chart data={data} />;
}02Check your understanding
Try it in your own words.
Explain when is useCallback useful in React without looking at the code. Then modify the intermediate example, describe one trade-off and identify when the real-world pattern fits.
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