What are impure pipes?

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Accepted Answer

Impure pipes in Angular are pipes that execute on every change detection cycle, regardless of whether the input value has changed or not. They are less performant than pure pipes but are necessary for certain scenarios.

Key characteristics of impure pipes:

1. Frequent Execution - Run on every change detection cycle
2. Stateful - Can maintain internal state
3. Performance Cost - Can slow down application if overused
4. Necessary for Dynamic Data - Required when input can change without reference change

Impure pipes are useful when you need to transform data that changes internally (like arrays or objects that mutate) or when you need to work with asynchronous data.

You should use impure pipes sparingly due to their performance impact.