Form state tracking (dirty, touched, valid) in Angular

Introduction

Form state tracking helps you know if a user has changed or interacted with a form field and if the input is valid. This makes forms smarter and friendlier.

When you want to show error messages only after a user has touched a field.

When you want to enable a submit button only if the form is valid and changed.

When you want to reset the form state after submission.

When you want to highlight fields that need attention based on user interaction.

Syntax

Angular

import { Component } from '@angular/core';
import { FormControl, Validators } from '@angular/forms';

@Component({
  standalone: true,
  selector: 'app-simple-form',
  template: `
    <input [formControl]="nameControl" aria-label="Name input" />
    <div *ngIf="nameControl.touched && nameControl.invalid" role="alert">
      Name is required.
    </div>
    <button [disabled]="!nameControl.dirty || nameControl.invalid">Submit</button>
  `
})
export class SimpleFormComponent {
  nameControl = new FormControl('', Validators.required);
}

dirty means the user changed the value from the original.

touched means the user focused and then left the field.

valid means the current value passes all validation rules.

Examples

True if the user changed the input value.

Angular

nameControl.dirty

True if the user focused and then blurred the input.

Angular

nameControl.touched

True if the input value meets all validators.

Angular

nameControl.valid

True if the input value fails any validator.

Angular

nameControl.invalid

Sample Program

This component tracks the state of an email input. It shows messages only after the user touches the field and if the email is invalid. The submit button is enabled only if the user changed the input and the email is valid.

Angular

import { Component } from '@angular/core';
import { FormControl, Validators } from '@angular/forms';

@Component({
  standalone: true,
  selector: 'app-form-state',
  template: `
    <label for="email">Email:</label>
    <input id="email" type="email" [formControl]="emailControl" aria-describedby="emailHelp" [attr.aria-invalid]="emailControl.invalid" />
    <div id="emailHelp" *ngIf="emailControl.touched && emailControl.invalid" role="alert" style="color: red;">
      Please enter a valid email.
    </div>
    <p>Dirty: {{emailControl.dirty}}</p>
    <p>Touched: {{emailControl.touched}}</p>
    <p>Valid: {{emailControl.valid}}</p>
    <button [disabled]="!emailControl.dirty || emailControl.invalid">Submit</button>
  `
})
export class FormStateComponent {
  emailControl = new FormControl('', [Validators.required, Validators.email]);
}

Important Notes

Use touched to avoid showing errors before the user interacts.

dirty helps to detect if the user made changes to the form.

Always combine these states to improve user experience in forms.

Summary

dirty means the user changed the input value.

touched means the user focused and left the input.

valid means the input passes validation rules.

Practice

1. In Angular forms, what does the dirty state indicate about a form control?

easy

A. The input has passed validation rules.

B. The user has changed the input value.

C. The user has focused and then left the input.

D. The form control is disabled.

Solution

1. Step 1: Understand the meaning of dirty in Angular forms

   The dirty state means the user has changed the value of the input from its original value.

2. Step 2: Compare with other states

   touched means the user focused and left the input, valid means the input passes validation, and disabled means the control is inactive.

3. Final Answer:

   The user has changed the input value. -> Option B

4. Quick Check:

   dirty = user changed input [OK]

Hint: Dirty means input value changed by user [OK]

Common Mistakes:

• Confusing dirty with touched state
• Thinking dirty means input is valid
• Assuming dirty means input is disabled

2. Which of the following is the correct way to check if a form control named email is touched in an Angular template?

easy

A. form.controls.email.touched

B. form.email.touched()

C. form.get('email').isTouched

D. form.controls['email'].isTouched()

Solution

1. Step 1: Recall Angular form control access syntax

   In Angular, form controls are accessed via form.controls.controlName or form.get('controlName'). The touched property is a boolean, not a method.

2. Step 2: Identify correct property usage

   form.controls.email.touched correctly accesses the touched property. Other options incorrectly use method calls or wrong property names.

3. Final Answer:

   form.controls.email.touched -> Option A

4. Quick Check:

   Access touched as property, not method [OK]

Hint: Use .controls.name.touched without parentheses [OK]

Common Mistakes:

• Using parentheses like a method on touched
• Using incorrect property names like isTouched
• Accessing controls incorrectly with dot vs bracket

3. Given this Angular reactive form control initialization:

this.form = new FormGroup({
  username: new FormControl('', Validators.required)
});

// User focuses on username input, types 'John', then leaves the input.

What will be the values of dirty, touched, and valid for username after these actions?

medium

A. dirty: true, touched: true, valid: false

B. dirty: false, touched: true, valid: true

C. dirty: true, touched: false, valid: false

D. dirty: true, touched: true, valid: true

Solution

1. Step 1: Analyze user actions on the form control

   User focused and left the input, so touched is true. User changed the value from empty string to 'John', so dirty is true.

2. Step 2: Check validation status

   The control has Validators.required. Since 'John' is not empty, the control is valid, so valid is true.

3. Final Answer:

   dirty: true, touched: true, valid: true -> Option D

4. Quick Check:

   Changed + left + valid input = dirty, touched, valid true [OK]

Hint: Changed input + left focus + valid value = all true [OK]

Common Mistakes:

• Assuming dirty is false if user leaves input
• Confusing touched with dirty
• Thinking valid is false if user typed anything

4. You have this Angular template snippet:

<input type="text" formControlName="email">
<div *ngIf="form.controls.email.dirty && form.controls.email.valid">Valid email changed!</div>

But the message never shows even after typing a valid email. What is the likely problem?

medium

A. The form control is not marked as touched, so the message won't show.

B. The valid property is misspelled and should be isValid.

C. The form control might have an email validator, so valid is false.

D. The dirty property does not update on user input.

Solution

1. Step 1: Understand the condition for showing the message

   The message shows only if the control is both dirty and valid.

2. Step 2: Check if validation is set up

   If the form control has an email validator but the input doesn't pass it (even if it looks valid), valid is false, so the message won't appear.

3. Final Answer:

   The form control might have an email validator, so valid is false. -> Option C

4. Quick Check:

   Missing validator means valid stays false [OK]

Hint: Check validators if valid never becomes true [OK]

Common Mistakes:

• Thinking touched affects this condition
• Using wrong property names like isValid
• Assuming dirty never updates on input

5. You want to disable the submit button in an Angular reactive form until the user has changed at least one input and all inputs are valid. Which condition correctly implements this logic in the template?

<button [disabled]="???">Submit</button>

hard

A. [disabled]="form.pristine || form.invalid"

B. [disabled]="!form.touched || !form.valid"

C. [disabled]="form.touched && form.valid"

D. [disabled]="!form.dirty && !form.valid"

Solution

1. Step 1: Understand form state properties

   pristine means no changes made, opposite of dirty. invalid means form is not valid.

2. Step 2: Translate requirement to condition

   Disable button if form is pristine (no changes) or invalid (not valid). So disable when form.pristine || form.invalid.

3. Final Answer:

   [disabled]="form.pristine || form.invalid" -> Option A

4. Quick Check:

   Disable if no changes or invalid [OK]

Hint: Disable if pristine or invalid to require change and validity [OK]

Common Mistakes:

• Using dirty instead of pristine incorrectly
• Confusing valid with invalid
• Using touched instead of dirty/pristine