Custom Validators in Angular

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As you’re building an Angular app and the built-in validators like required, email, and minLength just aren’t cutting it anymore. You need your form to do things like:

• Block usernames with special characters 😬
• Make sure passwords actually match 🤦‍♀️
• Check if someone is at least 18 🍺
• Validate an email domain (hello corporate apps) 💼

Enter: Custom Validators — your best friend when forms get real.

Let’s break it down and walk through some real-world, super practical examples of how you can make your Angular forms smarter using custom validators.

🛠️ What is a Custom Validator?

A custom validator is a function that returns either:

• null if the control is valid
• An error object like { customError: true } if the control is invalid

🔧 Writing a Simple Custom Validator

✅ Example 1: No Special Characters Allowed

ts
import { AbstractControl, ValidationErrors } from '@angular/forms';

export function noSpecialCharsValidator(control: AbstractControl): ValidationErrors | null {
  const forbidden =…