Which attribute on an input element ensures the browser will not submit unless a value is provided?

Which attribute on an input element ensures the browser will not submit unless a value is provided?

• A. autofocus
• B. readonly
• C. disabled
• D. required

Answer: (D)

The required attribute on an input enforces that a value must be provided before the form can be submitted. When this attribute is present, the browser performs constraint validation and will block submission if the field is empty, typically focusing that field and showing a message like “Please fill out this field.” This makes the form reject incomplete data, ensuring the user enters something before sending the form. Other attributes don’t enforce that behavior: autofocus just moves the cursor to the field on page load; readonly prevents editing but still includes the value when submitting; disabled removes the control from submission entirely.

The required attribute on an input enforces that a value must be provided before the form can be submitted. When this attribute is present, the browser performs constraint validation and will block submission if the field is empty, typically focusing that field and showing a message like “Please fill out this field.” This makes the form reject incomplete data, ensuring the user enters something before sending the form. Other attributes don’t enforce that behavior: autofocus just moves the cursor to the field on page load; readonly prevents editing but still includes the value when submitting; disabled removes the control from submission entirely.