reactive-range-control#reactive-range.ts

reactiveRange() {
    const startCtrl = this.form.get('rangeStart');
    const endCtrl = this.form.get('rangeEnd');

    startCtrl.valueChanges
      .pipe(filter(v => v > endCtrl.value))
      .subscribe(v => endCtrl.setValue(v));

    endCtrl.valueChanges
      .pipe(filter(v => v < startCtrl.value))
      .subscribe(v => startCtrl.setValue(v));
  }