How to check whether a form or a control is invalid or not in Angular 10 ?

In this article, we are going to check whether a form is invalid or not in Angular 10. invalid property is used to report that the control or the form is invalid or not.

Syntax:

form.invalid 

Return Value:

• boolean: the boolean value to check whether a form is invalid or not.

NgModule: Module used by the invalid property is:

• FormsModule

Approach: 

• Create the Angular app to be used.
• In app.component.html make a form using ngForm directive.
• In app.component.ts get the information using the invalid property.
• Serve the angular app using ng serve to see the output.

Example 1:

app.component.ts

import { Component } from '@angular/core';
import { FormGroup, FormControl, FormArray, Validators }
 from '@angular/forms'

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {
  form = new FormGroup({
    name: new FormControl(

    ),
    rollno: new FormControl()
});

get name(): any {
  return this.form.get('name');
}

onSubmit(): void {
  console.log("Form is invalid : ",this.form.invalid);
}
}

app.component.html

<form [formGroup]="form" (ngSubmit)="onSubmit()">
  <input formControlName="name" placeholder="Name">
<br>
<button type='submit'>Submit</button>
<br>
<br>
</form>

Output:

Reference: https://angular.io/api/forms/AbstractControlDirective#invalid