Validators (required, minLength, pattern) in Angular - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the Validators.required validator do in Angular forms?

It ensures that the form control has a value. The field cannot be empty or null for the form to be valid.

beginner

How does Validators.minLength(5) affect a form control?

It requires the input to have at least 5 characters. If fewer, the control is invalid.

beginner

What is the purpose of Validators.pattern in Angular?

It checks if the input matches a specific regular expression pattern, like a phone number or email format.

intermediate

How do you combine multiple validators on a single form control?

Use Validators.compose([validator1, validator2]) or pass an array like [Validators.required, Validators.minLength(3)].

beginner

What happens in the UI when a form control is invalid due to validators?

You can show error messages or disable buttons. Angular sets control.invalid to true, letting you react in the template.

Which validator ensures a form field is not left empty?

A Validators.maxLength

B Validators.minLength

C Validators.pattern

D Validators.required

Validators.required makes sure the field has a value.

What does Validators.minLength(8) check for?

A Input must be exactly 8 characters

B Input must match a pattern of 8 digits

C Input must be at least 8 characters

D Input must be less than 8 characters

It requires the input length to be 8 or more characters.

How do you apply multiple validators to one form control?

A Pass an array of validators

B Call validators one after another

C Use only one validator at a time

D Use <code>Validators.single()</code>

You pass an array like [Validators.required, Validators.minLength(3)].

Which validator would you use to check if input matches a phone number format?

A Validators.minLength

B Validators.pattern

C Validators.required

D Validators.email

Validators.pattern checks input against a regex pattern.

If a form control is invalid, what property becomes true?

A control.invalid

B control.touched

C control.valid

D control.dirty

control.invalid is true when validators fail.

Explain how you would use Validators.required, Validators.minLength, and Validators.pattern together on a form control.

Think about combining validators in the form control definition.

Describe how Angular form validation feedback works when a user enters invalid data.

Consider what happens behind the scenes and how the UI reacts.