QReact · Interview preparation
What does React.memo solve, and what does it not solve?
Know when memoization reduces work and when it simply adds complexity.
The idea to remember.
React.memo can skip rendering a component when its props are shallowly equal to the previous props. It does not stop renders caused by that component’s own state or context updates, and it is ineffective when parents recreate object or function props every render. Measure before applying it broadly.
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 what does React.memo solve, and what does it not solve 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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