Angular Reactuve Form Control valueChanges get value changed field name , prev value and current val

Instead of subscribing to theFormGroup.valueChanges observable, you could subscribe to the FormControl.valueChanges observable. See https://angular.io/api/forms/FormControl for the implementation. This way you could have access to the control itself. Maybe something like this?

Object.keys(this.form.controls).forEach(key => {
        this.form.controls[key].valueChanges.pipe(startWith(null), pairwise())
        .subscribe(([prev, next]: [any, any]) => {
            console.log(key) // your FormControl Identifier 
            console.log('PREV2', prev);
            console.log('NEXT2', next);
        });
    });