Explain template driven forms vs reactive forms in Angular

In Angular, there are two main approaches to handling forms: template-driven forms and reactive forms. Each approach has its own advantages and use cases, so understanding their differences is important for choosing the right one for your application.

Template-Driven Forms:

1. Binding and Validation: Template-driven forms rely heavily on directives in the template to create and manipulate the form structure. Directives such as ngModel, ngForm, ngSubmit, etc., are used to bind data and handle form validation directly in the template.

2. Simplicity and Quick Setup: Template-driven forms are easier and quicker to set up, especially for simple forms with basic validation requirements. They are more suitable for small forms where complex data manipulation or dynamic form controls are not heavily needed.

3. Two-Way Data Binding: They make use of Angular's two-way data binding with ngModel, where changes to the form elements in the template are automatically reflected in the underlying data model and vice versa.

4. Limitations: Template-driven forms can become difficult to manage and maintain as the form grows in complexity. They may not be as flexible for testing, especially when it comes to unit testing form logic.

5. Example:

<form (ngSubmit)="onSubmit()">

  <input type="text" name="name" [(ngModel)]="user.name" required>

  <button type="submit">Submit</button>

</form>

Reactive Forms:

1. Form Control Objects: Reactive forms are driven by instances of FormControl, FormGroup, and FormArray classes in the component code. These classes provide a more explicit and centralized approach to managing the state and behavior of forms.

2. Programmatic Control: Reactive forms offer more control and flexibility in managing form state and validation logic programmatically. Form controls are defined in the component class, enabling dynamic manipulation of form controls and validations.

3. Complex Forms: They are ideal for complex forms with dynamic fields, form groups, or forms that require extensive form manipulation and validation.

4. Immutability: Reactive forms encourage immutability, where form values and state changes are managed through pure functions and not directly mutated.

5. Example:

import { FormBuilder, FormGroup, Validators } from '@angular/forms';

export class MyComponent {

  myForm: FormGroup;

  constructor(private fb: FormBuilder) {

    this.myForm = this.fb.group({

      name: ['', Validators.required],

      email: ['', [Validators.required, Validators.email]],

      address: this.fb.group({

        street: [''],

        city: [''],

        state: ['']

      })

    });

  }

  onSubmit() {

    console.log(this.myForm.value);

  }

}

Choosing Between Template-Driven and Reactive Forms:

• Use Template-Driven Forms When:

  • The form is simple and doesn’t require complex validation.
  • You prefer working in the template with two-way data binding.
  • Rapid prototyping or a quick solution is needed.

• Use Reactive Forms When:

  • The form is complex and requires dynamic manipulation of form controls.
  • You need more control over validation logic and error handling.
  • You prefer a more scalable and testable approach, especially for larger applications.

In summary, while template-driven forms are simpler and quicker for basic forms, reactive forms offer more flexibility and control, making them suitable for complex forms and larger applications. The choice between them often depends on the specific requirements and complexity of the form in your Angular application.