Angular 10 Form Validation example (Reactive Forms)

In this tutorial, I will show you how to implement Angular 10 Form Validation example (and Submit) with Reactive Forms Module and Bootstrap 4.

Newer versions:
Angular 11 Form Validation example (Reactive Forms)
Angular 12 Form Validation example (Reactive Forms)

More Practice:
Angular 10 File upload example with progress bar
Angular 10 CRUD Application example with Web API
Angular 10 JWT Authentication example with Web Api

Serverless with Firebase:
Angular 10 Firebase CRUD Realtime Database
Angular 10 Firestore CRUD with AngularFireStore
Angular 10 File upload with Firebase Storage example


Overview of Angular 10 Form Validation example

We will implement validation for a Angular Form using Reactive Forms Module and Bootstrap. The form has:

  • Full Name: required
  • Username: required, from 6 to 20 characters
  • Email: required, email format
  • Password: required, from 6 to 40 characters
  • Confirm Password: required, same as Password
  • Accept Terms Checkbox: required

angular-10-form-validation-example-reactive-forms

Some fields could be wrong:

angular-10-form-validation-example-reactive-forms-check

Successful Submission will look like this:

angular-10-form-validation-example-reactive-forms-successful

Technology

We’re gonna use following modules:

  • Angular 10
  • Bootstrap 4
  • @angular/forms 10

Setup Project

First we need to add the ReactiveFormsModule into our App Module.

Open src/app/app.module.ts and import ReactiveFormsModule from @angular/forms:

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { ReactiveFormsModule } from '@angular/forms';

import { AppComponent } from './app.component';

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule,
    ReactiveFormsModule
  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule { }

Import Bootstrap 4

Open src/index.html and add following line to <head> tag:

<!doctype html>
<html lang="en">
<head>
  ...
  <link href="//netdna.bootstrapcdn.com/bootstrap/4.5.2/css/bootstrap.min.css" rel="stylesheet" />
</head>
<body>
  <app-root></app-root>
</body>
</html>

Form Validation with Angular 10 Reactive Forms

The app component contains Form Validation example built with the @angular/forms version 10.

Open app/app.component.ts, we’re gonna import necessary library first:

import { Component, OnInit } from '@angular/core';
import { AbstractControl, FormBuilder, FormGroup, Validators } from '@angular/forms';
import Validation from './utils/validation';

We use Angular FormBuilder to create a FormGroup object (form property) which is then bound to the template <form> element (using the [formGroup] directive later).

Validators provides a set of built-in validators (required, minLength, maxLength…) that can be used by form controls.

A validator is a function that processes a FormControl or collection of controls and returns an error map or null (meaning validation has passed).

Validation is our custom class that provides custom validator function. I will explain it later.

export class AppComponent implements OnInit {
  form: FormGroup;
  submitted = false;

  constructor(private formBuilder: FormBuilder) {}

  ngOnInit(): void {
    this.form = this.formBuilder.group(
      {
        fullname: ['', Validators.required],
        username: [
          '',
          [
            Validators.required,
            Validators.minLength(6),
            Validators.maxLength(20)
          ]
        ],
        email: ['', [Validators.required, Validators.email]],
        password: [
          '',
          [
            Validators.required,
            Validators.minLength(6),
            Validators.maxLength(40)
          ]
        ],
        confirmPassword: ['', Validators.required],
        acceptTerms: [false, Validators.requiredTrue]
      },
      {
        validators: [Validation.match('password', 'confirmPassword')]
      }
    );
  }

  ...
}

We also have getter f to access form controls (form.controls) from the template. For example, we can get username field in the template using f.username instead of form.controls.username.

The submitted property helps us to check whether the form is submitted or not.

export class AppComponent implements OnInit {
  form: FormGroup;
  submitted = false;

  constructor(private formBuilder: FormBuilder) {}

  ngOnInit(): void {
    ...
  }

  get f(): { [key: string]: AbstractControl } {
    return this.form.controls;
  }

  onSubmit(): void {
    this.submitted = true;

    if (this.form.invalid) {
      return;
    }

    console.log(JSON.stringify(this.form.value, null, 2));
  }

  onReset(): void {
    this.submitted = false;
    this.form.reset();
  }
}

Angular 10 Form Validation template

Now we create the form with input fields and validation messages.

We bind to the FormGroup object (form) in the app component using [formGroup] directive. Form submit event will call onSubmit() handler above using event binding (ngSubmit).

Validation messages will display after form submission for the first time by submitted property.

app/app.component.html

<div class="register-form">
  <form [formGroup]="form" (ngSubmit)="onSubmit()">
    <div class="form-group">
      <label>Full Name</label>
      <input
        type="text"
        formControlName="fullname"
        class="form-control"
        [ngClass]="{ 'is-invalid': submitted && f.fullname.errors }"
      />
      <div *ngIf="submitted && f.fullname.errors" class="invalid-feedback">
        <div *ngIf="f.fullname.errors.required">Fullname is required</div>
      </div>
    </div>

    <div class="form-group">
      <label>Username</label>
      <input
        type="text"
        formControlName="username"
        class="form-control"
        [ngClass]="{ 'is-invalid': submitted && f.username.errors }"
      />
      <div *ngIf="submitted && f.username.errors" class="invalid-feedback">
        <div *ngIf="f.username.errors.required">Username is required</div>
        <div *ngIf="f.username.errors.minlength">
          Username must be at least 6 characters
        </div>
        <div *ngIf="f.username.errors.maxlength">
          Username must not exceed 20 characters
        </div>
      </div>
    </div>

    <div class="form-group">
      <label>Email</label>
      <input
        type="text"
        formControlName="email"
        class="form-control"
        [ngClass]="{ 'is-invalid': submitted && f.email.errors }"
      />
      <div *ngIf="submitted && f.email.errors" class="invalid-feedback">
        <div *ngIf="f.email.errors.required">Email is required</div>
        <div *ngIf="f.email.errors.email">Email is invalid</div>
      </div>
    </div>

    <div class="form-group">
      <label>Password</label>
      <input
        type="password"
        formControlName="password"
        class="form-control"
        [ngClass]="{ 'is-invalid': submitted && f.password.errors }"
      />
      <div *ngIf="submitted && f.password.errors" class="invalid-feedback">
        <div *ngIf="f.password.errors.required">Password is required</div>
        <div *ngIf="f.password.errors.minlength">
          Password must be at least 6 characters
        </div>
        <div *ngIf="f.password.errors.maxlength">
          Username must not exceed 40 characters
        </div>
      </div>
    </div>

    <div class="form-group">
      <label>Confirm Password</label>
      <input
        type="password"
        formControlName="confirmPassword"
        class="form-control"
        [ngClass]="{ 'is-invalid': submitted && f.confirmPassword.errors }"
      />
      <div
        *ngIf="submitted && f.confirmPassword.errors"
        class="invalid-feedback"
      >
        <div *ngIf="f.confirmPassword.errors.required">
          Confirm Password is required
        </div>
        <div *ngIf="f.confirmPassword.errors.matching">
          Confirm Password does not match
        </div>
      </div>
    </div>

    <div class="form-group form-check">
      <input
        type="checkbox"
        formControlName="acceptTerms"
        class="form-check-input"
        [ngClass]="{ 'is-invalid': submitted && f.acceptTerms.errors }"
      />
      <label for="acceptTerms" class="form-check-label"
        >I have read and agree to the Terms</label
      >
      <div *ngIf="submitted && f.acceptTerms.errors" class="invalid-feedback">
        Accept Terms is required
      </div>
    </div>

    <div class="form-group">
      <button type="submit" class="btn btn-primary">Register</button>
      <button
        type="button"
        (click)="onReset()"
        class="btn btn-warning float-right"
      >
        Reset
      </button>
    </div>
  </form>
</div>

Confirm Password validation in Angular 10

Now we will use Angular Custom Validator to implement password and confirm password validation..

– First, the validator returns null (meaning validation has passed) if there is any error on the control that we want to check (confirm password).
– Then, the validator checks that two fields match or not and set error on checking control if validation fails.

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

export default class Validation {
  static match(controlName: string, checkControlName: string): ValidatorFn {
    return (controls: AbstractControl) => {
      const control = controls.get(controlName);
      const checkControl = controls.get(checkControlName);

      if (checkControl.errors && !checkControl.errors.matching) {
        return null;
      }

      if (control.value !== checkControl.value) {
        controls.get(checkControlName).setErrors({ matching: true });
        return { matching: true };
      } else {
        return null;
      }
    };
  }
}

Run Angular 10 Form Validation example

You can run our App with command: npm start.
If the process is successful, open Browser with Url: http://localhost:4200/ and check it.

Or run on Stackblitz:

Conclusion

Today we’ve built Angular 10 Form Validation example successfully with Reactive Forms Module & Bootstrap 4.

You can also use the Form Validation in following posts:
Angular 10 File upload example with progress bar
Angular 10 CRUD Application example with Web API
Angular 10 JWT Authentication example with Web Api

Happy learning! See you again.

Further Reading

Serverless with Firebase:
Angular 10 Firebase CRUD Realtime Database
Angular 10 Firestore CRUD with AngularFireStore
Angular 10 File upload with Firebase Storage example

Fullstack CRUD Application:
Angular 10 + Node.js Express + MySQL example
Angular 10 + Node.js Express + MongoDB example
Angular 10 + Node.js Express + PostgreSQL example
Angular 10 + Spring Boot + MySQL example
Angular 10 + Spring Boot + PostgreSQL example
Angular 10 + Spring Boot + MongoDB example
Angular 10 + Django example
Angular 10 + Django + MySQL example
Angular 10 + Django + PostgreSQL example
Angular 10 + Django + MongoDB example

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