Showing validation errors in Angular - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of showing validation errors in Angular forms?

Showing validation errors helps users understand what input is required or incorrect, guiding them to fix mistakes before submitting the form.

beginner

How do you check if a form control has an error in Angular?

You check if the control is invalid and if it has been touched or dirty using properties like control.invalid and control.touched or control.dirty.

beginner

What Angular directive helps display validation errors conditionally in templates?

The *ngIf directive is used to show validation error messages only when the control has errors and the user has interacted with it.

intermediate

Why is it important to check if a control is touched or dirty before showing errors?

To avoid showing errors before the user interacts with the form, which can be confusing or overwhelming. It improves user experience by showing errors only after input.

intermediate

How can you show different error messages for different validation errors on the same form control?

By checking specific error keys on the control's errors object, like required, minlength, or pattern, and displaying messages accordingly.

Which Angular property indicates if a form control has failed validation?

A valid

B invalid

C pristine

D untouched

The invalid property is true when the control fails validation.

What does the *ngIf directive do when showing validation errors?

A It submits the form

B It styles the form control

C It conditionally displays error messages based on control state

D It disables the form control

*ngIf shows or hides elements based on a condition, useful for showing errors only when needed.

Why should you check if a control is touched before showing errors?

A To reset the form

B To clear the input

C To disable the submit button

D To show errors only after user interaction

Checking touched ensures errors appear only after the user has tried to change the input.

Which of these is NOT a common validation error key in Angular?

A maxvalue

B minlength

C required

D pattern

maxvalue is not a standard Angular validation error key; max is used instead.

How do you access the errors of a form control in Angular?

A control.errors

B control.value

C control.status

D control.name

The errors property contains the validation errors for the control.

Explain how to show validation error messages for a form control in Angular templates.

Think about when and how to show messages only after user interaction.

Describe why it is important to check user interaction states like touched or dirty before showing validation errors.

Consider how users feel if errors appear immediately on page load.