QReact · Interview preparation
How does the React Profiler help performance work?
The Profiler shows which components rendered and how long React took to commit them.
The idea to remember.
The Profiler shows which components rendered and how long React took to commit them. Use it to locate repeated expensive work before introducing caching or memoization.
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 how does the React Profiler help performance work 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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