To prevent a user from submitting a form when an invalid value is entered, which approach is correct?

To prevent a user from submitting a form when an invalid value is entered, which approach is correct?

• A. In the validations parameter, use a boolean check that blocks submission directly.
• B. In the validations parameter, use an if statement that returns a text string when the value is not valid.
• C. Show a message on the form using a field error.
• D. Use a separate server-side validation step after submission.

Answer: (B)

Validations on input fields prevent submitting a form when the input is invalid by returning an error message. In Appian, the validations parameter for a field expects an expression that, if the value is invalid, returns a text string. That string becomes the inline error shown to the user and the submit action is blocked until the value passes validation. This gives immediate, actionable feedback and keeps invalid data from being sent to the server. Using a boolean check wouldn’t provide a user-facing message in the same way, and a separate server-side validation happens after submission, which doesn’t stop the initial submit. Returning a text in the validations expression is the standard, effective way to prevent submission when input is invalid.

Validations on input fields prevent submitting a form when the input is invalid by returning an error message. In Appian, the validations parameter for a field expects an expression that, if the value is invalid, returns a text string. That string becomes the inline error shown to the user and the submit action is blocked until the value passes validation. This gives immediate, actionable feedback and keeps invalid data from being sent to the server. Using a boolean check wouldn’t provide a user-facing message in the same way, and a separate server-side validation happens after submission, which doesn’t stop the initial submit. Returning a text in the validations expression is the standard, effective way to prevent submission when input is invalid.