Custom Validation
Implement robust custom validations.
Custom Validation is a free Angular Academy lesson on CoddyKit. This is lesson 3 of 3. Any 3 lessons of this learning path are free to read in full — after that, CoddyKit PRO unlocks every lesson, plus hands-on practice with a built-in code editor and a 24/7 AI tutor. It is part of the Angular Academy learning path, and your progress syncs across the web and the CoddyKit app. The Angular Academy course includes 3 lessons in total.
Custom Validation in Angular Forms
Learn how to implement custom validators to ensure robust form validation in your Angular applications.
What is Custom Validation?
Custom validators let you define your own validation logic beyond built-in validators like required or minlength.
Creating a Custom Validator
A custom validator is a simple function that returns null if valid or an object if invalid:
function forbiddenNameValidator(control: AbstractControl): { [key: string]: any } | null {
return control.value === 'admin' ? { 'forbiddenName': true } : null;
}Applying the Validator
Apply the custom validator to your form control:
this.myForm = new FormGroup({
username: new FormControl('', [forbiddenNameValidator])
});Displaying Validation Errors
Show error messages conditionally in your template based on validation state:
<div *ngIf="myForm.get('username').hasError('forbiddenName')">
Username 'admin' is not allowed.
</div>Using Validator Directives
Validators can also be used directly as directives for template-driven forms:
<input name="username" ngModel forbiddenName>Async Validators
Async validators let you perform validation involving asynchronous operations, such as server checks:
username: new FormControl('', null, [asyncValidator])Testing Custom Validators
Always test validators to ensure they behave correctly under different scenarios and edge cases.
Summary
You've learned how to build and apply custom validators for robust form validation in Angular. Excellent work!
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- Courses
- 38
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Frequently Asked Questions
Is the “Custom Validation” lesson free?
Yes — any 3 lessons of the Angular Academy learning path, including “Custom Validation”, are free to read in full here on the web. After that, CoddyKit PRO unlocks every lesson, plus interactive practice with a built-in code editor and a 24/7 AI tutor. The Angular Academy course includes 3 lessons in total.
What will I learn in “Custom Validation”?
Implement robust custom validations. You practise Angular Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Angular Academy?
No prior experience is required. Angular Academy on CoddyKit is structured for beginners through advanced learners, so you can start here or from the beginning and move at your own pace. This is lesson 3 of 3.
How long does the “Custom Validation” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Angular Academy lesson?
Yes. Every Angular Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Template-driven Forms
- Reactive Forms
- Custom Validation