What are the differences between template driven forms and reactive forms in angular 2

Simply we can say

Reactive form can be used in the following situation

• Complex forms with more number of fields.
• Multiple complex validation are there. Custom validations are required
• Require JSON structure to be send with the values in the form.

We can get entire form in a structured way by using "form.value"

If we have 4 fields First Name, Last Name, Email, Phone Number in reactive form.

HTML code will be

<form [formGroup]="form">
    First Name <input formControlName="firstName">
    Last Name <input formControlName="lastName">
    Email <input formControlName="email">
    Phone Number <input formControlName="phoneNumber">
</form>

We can get the values from the form like below

{
"firstName": "FName",
"lastName": "LName",
"email": "test@123.com",
"phoneNumber": "123"
}

by calling form.value, where form is FormGroup Variable that we created.

Template Driven Form : It can be used when using simple forms. Like login page. With the two way data binding. We can simply assign value to variable from ui and vice versa.

Simple example is if we are givng two way binding for the below input.

<input [(ngModel)]="username">

We can simply display the value that user is giving in the UI.

<p>Hello {{username}}!</p>

A comprehensive answer to a similar question can be found here: What are the practical differences between template-driven and reactive forms?

here is what Aravind is posted which is abstract and direct to the point. so I copy and paste the entire comparison:

Template Driven Forms Features

• Easy to use
• Suitable for simple scenarios and fails for complex scenarios
• Similar to AngularJS
• Two way data binding(using [(NgModel)] syntax)
• Minimal component
• Automatic track of the form and its data(handled by Angular)
• Unit testing is another challenge

Reactive Forms Features

• More flexible, but needs a lot of practice

• Handles any complex scenarios

• No data binding is done (immutable data model preferred by most developers)

• More component code and less HTML markup

• Reactive transformations can be made possible such as

  • Handling a event based on a debounce time

  • Handling events when the components are distinct until changed

  • Adding elements dynamically

• Easier unit testing

A side by side pros and cons