Answer
Pure Pipes: Run only when input changes, fast and cached.
Impure Pipes: Run on every change detection cycle, can slow performance.
Impure pipes are needed only when data mutates without reference change.
Quick Answer
Pure pipes: run only when input reference changes (default). Angular caches the result - same input = same output = no recomputation. Impure pipes: run on every change detection cycle regardless of input changes. Impure pipes are expensive and should be avoided for frequently rendering components. Use impure pipes only when necessary (e.g., async pipe which must track subscriptions).
S
SugharaIQ Editorial Team
Verified Answer
This answer has been peer-reviewed by industry experts holding senior engineering roles to ensure technical accuracy and relevance for modern interview standards.
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Source: SugharaIQ