If you try to save a contact with either an invalid birthday, or an empty phone number, address, email, or social profile username, while your browser's debug console is open, you will see that the HTTP endpoint rejects the request with a 400 Bad Request response. This is because the backend performs some validation on the contact being created or updated.

Having a remote service performing some form of validation is pretty common; the opposite is actually considered bad architecture, as a remote service should not trust its clients for valid data. However, in order to provide a better end user experience, it is common to see validation also performed by client applications.

Aurelia offers the aurelia-validation library, which defines ...

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