How [ngModel] and (ngModelChange) work together?

Question

I am new to angular and I am learning Angular 6. I understood about ngModel. But while I was experimenting with ngModelChange, some questions raised.

I have an html element HTML

<input #input  type="text" [value]="name" [(ngModel)] ="name" (ngModelChange) ="change(input.value)"/>

Typescript

change(event :any) {
    this.name = event;
    console.log(this.name);
}

Upon changing the value in the input , I can see the changes with the name property.

When I changed the html code to

HTML

<input #input type="text" [value]="name"  [ngModel] ="name" 
(ngModelChange)="change(input.value)" />
{{ name }}

TS

change(event :any) {
    this.name = event;
    console.log(this.name);
}

It's working fine as expected in the console and in the UI.

Question 1

<input #input  type="text" [value]="name" [(ngModel)] ="name" 
(ngModelChange) ="change(input.value)"/>

&

<input #input type="text" [value]="name"  [ngModel] ="name" 
(ngModelChange)="change(input.value)" />

are same??

Question 2.

When I remove the [ngModel] directive. The ngModelChange is not getting triggered. Is it mandatory to have [ngModel]? If yes,Why?

HTML

<input #input type="text" [value]="name" 
(ngModelChange)="change(input.value)" />
<br/>
<br/>
{{ name }}

TS

change(event: any) {
     this.name = event;
     console.log(this.name);
 }

This would be a great help. Thanks in Advance.

Answer 1

The [()] syntax is easy to demonstrate when the element has a settable property called x and a corresponding event named xChange. Here's a SizerComponent that fits this pattern. It has a size value property and a companion sizeChange event

https://angular.io/guide/template-syntax#basics-of-two-way-binding

So, they are equivalent.

<input [(ngModel)]="name"/>
<input [ngModel]="name" (ngModelChange) ="name = $event"/>

But if there is no corresponding property, then xChange will not work.

<input (ngModelChange) ="name = $event"/>