Your first custom validator in Angular signal forms (step-by-step)

Yes, you can still use custom validators with Signal Forms, and they’re easier to add than you'd think. 🚀 Want to master Angular Signal Forms? I just released a full course where we build a real Signal Form step-by-step covering validation, async validation, dynamic fields, custom controls, and submission patterns. 👉 Enroll here (launch price $9.99 for 5 days): https://www.udemy.com/course/angular-signal-forms/?couponCode=021409EC66FC6440B867 Angular’s new Signal Forms API is here, and in this tutorial we rebuild a full Reactive Forms example using custom validators, Angular validation, and real-world form errors. You’ll see how to migrate Reactive Forms to Signal Forms, rewrite your Angular custom validators, and set up required, format, and length checks using the new validate() and customError() utilities. This is an Angular tutorial focused on practical, everyday problems, perfect for anyone upgrading to Angular 21 or exploring Angular signals for the first time. We’ll walk step-by-step through building a form model with signals, wiring fields using the new [field] directive, and creating reactive error messages that respond instantly to user input. Along the way, you’ll learn how Angular form signals simplify state management, how to implement a multi-rule Angular username validator, and why Signal Forms make form validation easier, cleaner, and more type-safe than ever. If you want to understand Reactive Forms vs Signal Forms and how to build better forms with the new Signal Forms API, this video will get you there fast. ------------------------------------------------------------------------------ 🔔 Subscribe for more Angular tutorials & tips → [🔗 https://www.youtube.com/c/briantreese?sub_confirmation=1] 👍 Like this video if you found it helpful, it really helps support the channel! ------------------------------------------------------------------------------ 🔗 Demo Links: - Before (https://stackblitz.com/edit/stackblitz-starters-klfvvxxw?file=src%2Fform%2Fform.component.ts) - After (https://stackblitz.com/edit/stackblitz-starters-hmhboefo?file=src%2Fform%2Fform.component.ts) ------------------------------------------------------------------------------ 📚 Additional Resources: - Signal Forms API (Experimental): https://github.com/angular/angular/tree/main/packages/forms/signals - Angular Reactive Forms Docs: https://angular.dev/guide/forms/reactive-forms - Angular Signals Overview: https://angular.dev/guide/signals - My course "Angular: Styling Applications": https://www.pluralsight.com/courses/angular-styling-applications - My course "Angular in Practice: Zoneless Change Detection": https://app.pluralsight.com/library/courses/angular-practice-zoneless-change-detection ------------------------------------------------------------------------------ 🎓 Angular Certification (New) If you’re looking to validate your Angular skills, there’s now an official certification built and reviewed by Google Developer Experts. It covers modern Angular concepts and is one of the first structured ways to demonstrate real-world Angular knowledge. 👉 https://certificates.dev/angular?friend=TREESE (They’re currently offering up to 50% off) ------------------------------------------------------------------------------ 📖 Chapters: 0:00 – Introduction 0:31 – Preview: Reactive Form Validation Behavior 1:59 – How the Reactive Version Works (FormGroup + Validators) 5:32 – What is Angular Signal Forms? (Experimental Overview) 6:01 – Migrating: Reactive Forms → Signal Forms 6:36 – Build the Form with form() + a Signal Model 7:55 – Custom Validators in Signal Forms (validate() + customError()) 9:42 – Error Handling with Computed Signals 11:35 – Rewriting the Template with [field] + Signals 12:38 – Live Test (Required, Format, and Length Validation) 13:38 – Takeaway: Custom Validators Work Great in Signal Forms ------------------------------------------------------------------------------ 🧰 About the Tools Used This video uses Angular Signal Forms, an experimental API that introduces signal-based form state and validation. Features demonstrated include form(), signal-backed models, the Field directive, and the new validate() and customError() functions for building custom validators. Error messages are handled using Angular’s computed signals for cleaner, reactive UI updates. ------------------------------------------------------------------------------ #angular #angular21 #signalforms #angularsignals #webdevelopment #frontend #typescript #customvalidators #angulardeveloper #codingtutorial