Angular
Enhancing Angular Forms with Custom Validation
Why Use Custom Validation?
- Improves User Experience by guiding users with meaningful error messages.
- Enforces Business Rules that default validators may not cover.
- Reusable Logic across multiple forms.
How to Implement Custom Validation
1. Create a Custom Validator
Define a function that returns an error object if validation fails.
import { AbstractControl, ValidationErrors, ValidatorFn } from '@angular/forms';export function strongPasswordValidator(): ValidatorFn { return (control: AbstractControl): ValidationErrors | null => { const value = control.value; if (!/[A-Z]/.test(value) || !/[0-9]/.test(value) || value.length < 8) { return { strongPassword: true }; } return null; };}
2. Apply the Validator to a Form Control
this.form = new FormGroup({ password: new FormControl('', [Validators.required, strongPasswordValidator()])});
3. Display Error Messages in the Template
<input type="password" formControlName="password"><div *ngIf="form.controls.password.errors?.strongPassword"> Password is weak.</div>
Importing Necessary Modules
Angular provides built-in animation support through @angular/animations, but for more control, we use Element.animate() from WAAPI.
Best Practices
- Keep Validators Generic so they can be reused.
- Use Async Validators for server-side validation like checking email uniqueness.
- Provide Clear Error Messages to help users correct input easily.
Custom validation enhances form usability and ensures data integrity in Angular applications.
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