Angular 8 Forms Tutorial - Reactive Forms Validation Example
In this article, you’'ll see a quick example of how to setup form validation in Angular 8 using Reactive Forms.
The example is a simple registration form with pretty standard fields for title, first name, last name, email, password, confirm password and an accept Ts & Cs checkbox. All fields are required including the checkbox, the email field must be a valid email address and the password field must have a min length of 6. There’s also a custom validator called MustMatch which is used to validate that the confirm password and password fields match.
I’ve setup the form to validate on submit rather than as soon as each field is changed, this is implemented with a submitted property in the app component that is set to true when the form is submitted for the first time, and reset to false if the cancel button is clicked.
Styling of the example is all done with Bootstrap 4.3 CSS.
See on StackBlitz at https://stackblitz.com/edit/angular-8-reactive-form-validation
Reactive Forms Validation App Component
The app component defines the form fields and validators for our registration form using an Angular FormBuilder to create an instance of a FormGroup that is stored in the registerForm property. The registerForm is then bound to the form in the app template below using the [formGroup] directive.
I also added a getter f as a convenience property to make it easier to access form controls from the template. So for example you can access the confirmPassword field in the template using f.confirmPassword instead of registerForm.controls.confirmPassword.
import { Component, OnInit } from '@angular/core';
import { FormBuilder, FormGroup, Validators } from '@angular/forms';
// import custom validator to validate that password and confirm password fields match
import { MustMatch } from './_helpers/must-match.validator';
@Component({ selector: 'app', templateUrl: 'app.component.html' })
export class AppComponent implements OnInit {
registerForm: FormGroup;
submitted = false;
constructor(private formBuilder: FormBuilder) { }
ngOnInit() {
this.registerForm = this.formBuilder.group({
title: ['', Validators.required],
firstName: ['', Validators.required],
lastName: ['', Validators.required],
email: ['', [Validators.required, Validators.email]],
password: ['', [Validators.required, Validators.minLength(6)]],
confirmPassword: ['', Validators.required],
acceptTerms: [false, Validators.requiredTrue]
}, {
validator: MustMatch('password', 'confirmPassword')
});
}
// convenience getter for easy access to form fields
get f() { return this.registerForm.controls; }
onSubmit() {
this.submitted = true;
// stop here if form is invalid
if (this.registerForm.invalid) {
return;
}
// display form values on success
alert('SUCCESS!! :-)\n\n' + JSON.stringify(this.registerForm.value, null, 4));
}
onReset() {
this.submitted = false;
this.registerForm.reset();
}
}
Reactive Forms Validation App Template
The app component template contains all the html markup for displaying the example registration form in your browser. The form element uses the [formGroup] directive to bind to the registerForm FormGroup in the app component above.
The form binds the form submit event to the onSubmit() handler in the app component using the Angular event binding (ngSubmit)="onSubmit()". Validation messages are displayed only after the user attempts to submit the form for the first time, this is controlled with the submitted property of the app component.
The cancel button click event is bound to the onReset() handler in the app component using the Angular event binding (click)="onReset()".
##### Angular 8 Reactive Form Validation
Title
Mr
Mrs
Miss
Ms
Title is required
First Name
First Name is required
Last Name
Last Name is required
Email
Email is required
Email must be a valid email address
Password
Password is required
Password must be at least 6 characters
Confirm Password
Confirm Password is required
Passwords must match
Accept Terms & Conditions
Accept Ts & Cs is required
Register
Cancel
Reactive Forms Custom “Must Match” Validator
The custom MustMatch validator is used in this example to validate that both of the password fields - password and confirmPassword - are matching. However it can be used to validate that any pair of fields is matching (e.g. email and confirm email fields).
It works slightly differently than a typical custom validator because I’m setting the error on the second field instead of returning it to be set on the formGroup. I did it this way because I think it makes the template a bit cleaner and more intuitive, the mustMatch validation error is displayed below the confirmPassword field so I think it makes sense that the error is attached the the confirmPassword form control.
import { FormGroup } from '@angular/forms';
// custom validator to check that two fields match
export function MustMatch(controlName: string, matchingControlName: string) {
return (formGroup: FormGroup) => {
const control = formGroup.controls[controlName];
const matchingControl = formGroup.controls[matchingControlName];
if (matchingControl.errors && !matchingControl.errors.mustMatch) {
// return if another validator has already found an error on the matchingControl
return;
}
// set error on matchingControl if validation fails
if (control.value !== matchingControl.value) {
matchingControl.setErrors({ mustMatch: true });
} else {
matchingControl.setErrors(null);
}
}
}
Reactive Forms Validation App Module
There isn’t much going on in the app module other than the standard stuff, the main thing you need to remember for using reactive forms in Angular is to import the ReactiveFormsModule from '@angular/forms' and include it in the imports array of the @NgModule decorator.
import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { ReactiveFormsModule } from '@angular/forms';
import { AppComponent } from './app.component';
@NgModule({
imports: [
BrowserModule,
ReactiveFormsModule
],
declarations: [
AppComponent
],
bootstrap: [AppComponent]
})
export class AppModule { }
#angular #forms
