useControlDirty

Returns whether an AbstractControl is dirty (has been modified) as a signal. The signal updates reactively whenever the control's dirty state changes. Works with FormControl, FormGroup, and FormArray.

Usage

import { useControlDirty } from 'ng-reactive-utils';

@Component({
  template: `
    <input [formControl]="nameControl" />

    @if (isDirty()) {
      <span class="modified-indicator">*</span>
    }
  `,
})
class EditableFieldComponent {
  nameControl = new FormControl('');
  isDirty = useControlDirty(this.nameControl);
}

Advanced Usage

import { useControlDirty } from 'ng-reactive-utils';

@Component({
  template: `
    <input [formControl]="titleControl" />
    <textarea [formControl]="contentControl"></textarea>

    @if (hasChanges()) {
      <button (click)="save()">Save Changes</button>
      <button (click)="revert()">Discard</button>
    }
  `,
})
class DocumentEditorComponent {
  titleControl = new FormControl('');
  contentControl = new FormControl('');

  titleDirty = useControlDirty(this.titleControl);
  contentDirty = useControlDirty(this.contentControl);

  hasChanges = computed(() => this.titleDirty() || this.contentDirty());
}

Parameters

Parameter	Type	Default	Description
control	AbstractControl	required	The control to check dirty state for

Returns

Signal<boolean> - A readonly signal containing the dirty state (true if modified)

Notes

• Works with FormControl, FormGroup, and FormArray
• Uses toSignal with control.valueChanges observable
• Returns true when the control value has been changed
• Returns false when the control is pristine (unchanged)
• Useful for tracking unsaved changes

Source

import { Signal } from '@angular/core';
import { toSignal } from '@angular/core/rxjs-interop';
import { AbstractControl } from '@angular/forms';
import { map } from 'rxjs';

/**
 * Returns whether an AbstractControl is dirty (has been modified) as a signal.
 * The signal updates reactively whenever the control's dirty state changes.
 * Works with FormControl, FormGroup, and FormArray.
 *
 * @param control - The AbstractControl to check dirty state for
 * @returns A signal containing the dirty state (true if modified)
 *
 * @example
 * ```typescript
 * @Component({
 *   template: `
 *     <input [formControl]="nameControl" />
 *     @if (isDirty()) {
 *       <span>Field has been modified</span>
 *     }
 *   `
 * })
 * class MyComponent {
 *   nameControl = new FormControl('');
 *   isDirty = useControlDirty(this.nameControl);
 * }
 * ```
 */
export const useControlDirty = (control: AbstractControl): Signal<boolean> => {
  return toSignal(control.valueChanges.pipe(map(() => control.dirty)), {
    initialValue: control.dirty,
  }) as Signal<boolean>;
};