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Angular Validator functions - Async and Sync Validators

What are the Validator functions?
There are two types of validator functions which are the following -
1.       Async validators
2.       Sync validators

Async validator functions that take a control instance and return an observable that later emits a set of validation errors or null.

Sync validator functions that take a control instance and return a set of validation errors or null.
Angular runs only Async validators due to some performance issues.

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