-
- Joined
- Mar 22, 2026
-
- Messages
- 434
-
- Reaction score
- 10
-
- Points
- 0
Performance bottlenecks in React applications often stem from unnecessary re-renders of heavy component sub-trees. When a parent component updates its state, all of its children re-render by default, which can lead to UI lag if those children perform expensive calculations on every render pass.
The
How useMemo Works
The hook accepts two arguments: a "create" function and an array of dependencies.
React will re-run the calculation only when either
When to Use It
1. Expensive Mathematical Operations: If you are filtering, sorting, or mapping through massive arrays of data.
2. Referential Equality: Passing objects or arrays down as props to child components wrapped in
Common Pitfalls
Do not wrap every single function or variable in
The
useMemo hook provides a way to cache the results of expensive computations between renders. By memoizing a value, React skips recalculating it unless one of its explicit dependencies changes.How useMemo Works
The hook accepts two arguments: a "create" function and an array of dependencies.
JavaScript:
const memoizedValue = useMemo(() => {
return computeExpensiveValue(a, b);
}, [a, b]);React will re-run the calculation only when either
a or b changes. If the dependencies remain identical to the previous render, useMemo returns the previously cached result instantly.When to Use It
1. Expensive Mathematical Operations: If you are filtering, sorting, or mapping through massive arrays of data.
2. Referential Equality: Passing objects or arrays down as props to child components wrapped in
React.memo to prevent cascading updates.Common Pitfalls
Do not wrap every single function or variable in
useMemo. Memoization itself has an overhead (memory to store the cached value and dependency array comparisons on every render). Only use it when you have a measurable performance bottleneck.