使用响应式表单侦听表单中的更改值

Question

Is there a way to listen for changes (only) in FormGroup With changes, I mean only the exact key and value that changed?

For example if the input name changes, something like {name: //newValue} should be emmitet

A Solution I don't prefer is to subscribe to valueChanges of every single FormControl.

I provided a little example for testing here .

Answer 1

您可以在FormGroup上订阅valueChanges ，但是您必须检查各个值以了解哪个FormControl的值已更改。

Answer 2

you can use pairwise

  .pipe(
   startWith({}),
   pairwise()
    ,tap(([previousValue, currentValue]) => {
    /** compare values here */
})
)
;

or

 .pipe(
   startWith({}),
   pairwise()
)
.subscribe(([previousValue, currentValue]) => {
    /** compare values here */
});