angular 8 定义的流不生效，能帮着分析一下吗？
const age$ =Observable.prototype.pipe(
combineLatest(ageNum$,ageUnit$, (_n, _u) => {
return this.toDate({age: n, unit: u}
);
}),
map((d => {
return {date: d, from: ‘age’};
}
)),
filter( => this.form.get(‘age’).valid)
);
const merged$ = Observable.prototype.pipe(
merge(birthday$,age$),
filter( => this.form.valid));

this.sub = merged$.subscribe(d => {

  const age = this.toAge(format(d.date,this.format));
  console.log(d.from);
  if (d.from === 'birthday') {
    if(age.age !== ageNum.value) {
      ageNum.patchValue(age.age, {emitEvent: false});
    }
    if(age.unit !== ageUnit.value) {
      this.selectedUnit = age.unit;
      ageUnit.patchValue(age.unit, {emitEvent: false});
    }
    this.propagateChange(d.date);
  } else {
    console.log('birthday.value : ' + birthday.value );
    const ageToCompare = this.toAge(format(birthday.value,this.format));
    
    if(age.age !== ageToCompare.age || age.unit !== ageToCompare.unit) {
      birthday.patchValue(d.date, {emitEvent: false});
      this.propagateChange(d.date);
    }
  }
}