PureComponents

PureComponents is a term used in software design to describe components that render output solely from their input properties and internal state, without relying on or mutating external state. A pure component is typically deterministic: given the same inputs, it produces the same output. This purity facilitates reasoning about code, simplifies testing, and supports predictable behavior in complex systems.

In user interface development, pure components are often optimized to avoid unnecessary work. Frameworks implement this by performing comparisons of a component’s inputs and re-rendering only when meaningful changes occur. In React, for example, the concept is embodied by the React.PureComponent class and by function components wrapped with memo, both of which rely on shallow comparisons of props and state to determine whether an update is needed.

Advantages of pure components include potential performance improvements in large component trees, easier unit testing due to predictable rendering, and better suitability for caching and memoization strategies. Limitations include the risk that shallow comparisons may miss deep mutations, which can lead to stale outputs if immutability is not preserved. They also require disciplined state management and sometimes additional boilerplate or tooling to ensure data structures are treated as immutable.

PureComponents are widely applicable in UI layers and other domains where components or modules produce outputs based only on their inputs. The term is often used to describe a pattern rather than a specific library, though particular frameworks provide explicit support through corresponding constructs such as memoization or pure-render components.

See also: pure function, immutability, React.PureComponent, memoization.