(change) vs (ngModelChange) 角度

Question

Angular 1 does not accept onchange() event, it's only accepts ng-change() event.

Angular 2, on the other hand, accepts both (change) and (ngModelChange) events, which both seems to be doing the same thing.

What's the difference?

which one is best for performance?

ngModelChange :

<input type="text" pInputText class="ui-widget ui-text"
    (ngModelChange)="clearFilter()" placeholder="Find"/>

vs change :

<input type="text" pInputText class="ui-widget ui-text" 
    (change)="clearFilter()" placeholder="Find"/>

Answer 1

(change) event bound to classical input change event.

https://developer.mozilla.org/en-US/docs/Web/Events/change

You can use (change) event even if you don't have a model at your input as

<input (change)="somethingChanged()">

(ngModelChange) is the @Output of ngModel directive. It fires when the model changes. You cannot use this event without ngModel directive.

https://github.com/angular/angular/blob/master/packages/forms/src/directives/ng_model.ts#L124

As you discover more in the source code, (ngModelChange) emits the new value.

https://github.com/angular/angular/blob/master/packages/forms/src/directives/ng_model.ts#L169

So it means you have ability of such usage:

<input (ngModelChange)="modelChanged($event)">

modelChanged(newObj) {
    // do something with new value
}

Basically, it seems like there is no big difference between two, but ngModel events gains the power when you use [ngValue] .

  <select [(ngModel)]="data" (ngModelChange)="dataChanged($event)" name="data">
      <option *ngFor="let currentData of allData" [ngValue]="currentData">
          {{data.name}}
      </option>
  </select>

dataChanged(newObj) {
    // here comes the object as parameter
}

assume you try the same thing without " ngModel things"

<select (change)="changed($event)">
    <option *ngFor="let currentData of allData" [value]="currentData.id">
        {{data.name}}
    </option>
</select>

changed(e){
    // event comes as parameter, you'll have to find selectedData manually
    // by using e.target.data
}

Answer 2

在 Angular 7 中， (ngModelChange)="eventHandler()"将在绑定到[(ngModel)]="value"值更改之前触发，而(change)="eventHandler()"将在绑定到的值之后触发[(ngModel)]="value"已更改。

Answer 3

As I have found and wrote in another topic - this applies to angular < 7 (not sure how it is in 7+)

Just for the future

we need to observe that [(ngModel)]="hero.name" is just a short-cut that can be de-sugared to: [ngModel]="hero.name" (ngModelChange)="hero.name = $event" .

So if we de-sugar code we would end up with:

<select (ngModelChange)="onModelChange()" [ngModel]="hero.name" (ngModelChange)="hero.name = $event">

or

<[ngModel]="hero.name" (ngModelChange)="hero.name = $event" select (ngModelChange)="onModelChange()">

If you inspect the above code you will notice that we end up with 2 ngModelChange events and those need to be executed in some order.

Summing up: If you place ngModelChange before ngModel , you get the $event as the new value, but your model object still holds previous value. If you place it after ngModel , the model will already have the new value.

SOURCE

Answer 4

1 - (change) is bound to the HTML onchange event. The documentation about HTML onchange says the following :

Execute a JavaScript when a user changes the selected option of a <select> element

Source : https://www.w3schools.com/jsref/event_onchange.asp

2 - As stated before, (ngModelChange) is bound to the model variable binded to your input.

So, my interpretation is :

• (change) triggers when the user changes the input
• (ngModelChange) triggers when the model changes, whether it's consecutive to a user action or not

Answer 5

As per my experience (change) and (ngModelChange) has two different usage.

1. (ngModelChange) triggers when HTML renders, user changed the value of that element.

2. (change) triggers when user changes the value and leave the element focus.

Usage:

1. (ngModelChange) : when you have critical things that depends on html any type of changes that you have to handle.
2. (change) : When you have to handle only value changes done by user.

Note: Be careful while using the (ngModelChange) because sometimes it will give you maximum call stack issue and your form will stuck.