如何在角度ngModel中比较旧值和新值

Question

以下是代码：

.HTML：

 <input type="text" [(ngModel)]="car.name"/>
 <button (click) = "save()" ></buton>
 {{car.name}} // the init value is "BWM" from Ajax;

TS：

car = new Car();
ngOnInit(){
 // eg: I get the car.name from here. The car.name = "BMW";
 this.http.get('/data').subscribe(car => this.car = car);
}
save(){
  //  Here how I compare the car.name with "BMW" ?
}
class Car{
   constructor(private string name){}
}

car.name 总是变化，因为我使用ngModel。我想将其与第一个值"BWM"进行比较。我正在学习角度形式.如何使用？还是使用 Rxjs？

我不能接受这个：

 car2 = new Car();
 save() {
      this.car2 = JSON.parse(JSON.stringify(car));
      if(car.name == car2.name)
         console.log("the name is BWM");
      }else{
         console.log("the name isn't BWM");
  }

Answer 1

我会说为此使用单独的对象：

.HTML：

...
<input type="text" [(ngModel)]="inputCarName"/>
...

TS：

car = new Car();
inputCarName: string;
ngOnInit(){
 // eg: I get the car.name from here. The car.name = "BMW";
 this.http.get('/data').subscribe(car => this.car = car);
}
save(){
  //  Here how I compare the car.name with "BMW" ?
  if(inputCarName == this.car.name)
  {
    //...whatever
  }
  
}
class Car{
   constructor(private string name){}
}

Answer 2

所以如果你想将旧值与最新值进行比较，请在输入中添加一个变量，例如

[(ngModel)]="myModel" #newvalue (change)="changeEvent(newvalue.value)"

和打字稿

changeEvent(newValue) {
  console.log(newValue, this.myModel);
}

希望这有帮助。 在此处查找详细的使用角度模板引用变量