Angular2 ngModelChange previous value

问题

Is there a way to get the previous(last) value of a field on ngModelChange? What I have goes something like this

HTML

<input type="text" [(ngModel)]="text" (ngModelChange)="textChanged($event)">

Handler

private textChanged(event) {
    console.log('changed', this.text, event);
}

What I get is

changed *newvalue* *newvalue*

Of course I can keep the older value using another variable, but is there a better way?

回答1:

What you can do is,

DEMO : http://plnkr.co/edit/RXJ4D0YJrgebzYcEiaSR?p=preview

<input type="text" 
       [ngModel]="text"                      //<<<###changed [(ngModel)]="text" to [ngModel]="text"
       (ngModelChange)="textChanged($event)"> 

private textChanged(event) {        
    console.log('changed', this.text, event);
    this.text=event;                          //<<<###added 
}

回答2:

So found kinda weird(at least for me) possible solution for this with least changes in the code in question. So on assigning the (ngModelChange) attribute before [(ngModel)] what I get is following with the same handler:

changed *older value* *new value*

I get the new value in this.textlike so:

setTimeout(() => console.log(this.text), 0);

回答3:

all you need to do is to put (ngModelChange)="textChanged($event)" to the left of [(ngModel)] element in the html tag, like:

<input (whatever...) (ngModelChange)="textChanged($event)" [(ngModel)]="text">

This way, inside textChanged(event), the element you are binding to still has the previous value, while event is the new one

回答4:

<input (ngModelChange)="preTextChanged($event)" [(ngModel)]="text" (ngModelChange)="postTestChanged($event)">

In this way you can know the previous value and the next value

来源：https://stackoverflow.com/questions/40172351/angular2-ngmodelchange-previous-value

标签

angular

angular2-ngmodel