Angular Rxjs - 条件运算符

Question

I have a function that has three parameters: an id that I need as parameters for invoking the addEvent service, and other two parameters, two arrays that contains a list of people to add or remove to the event that I'm creating. I must check if these arrays are empty or not to invoking some services. I write it, but I don't like really much:

addEvent(id: number, newPeople: any[], peopleToRemove: any[]) {
  this.eventService.addEvent(id).pipe( mergeMap(res => {
    if(newPeople.length > 0 && peopleToRemove.length > 0) {
     return forkJoin([this.eventService.addPeople(res.id, newPeople), this.eventService.removePeople(res.id, peopleToRemove)])
    }
    else if(newPeople.length > 0 && peopleToRemove.length === 0) {
     return this.eventService.addPeople(res.id, newPeople)
    }
    else if(peopleToRemove.length > 0 && newPeople.length === 0) {
     return this.eventService.removePeople(res.id, peopleToRemove)
  })).subscribe(res => {
    if(newPeople.length) { 
      //doing something 
    }
    if(peopleToRemove.length) {
     //doing something 
    }
  })
}

Is there an rxjs operator for doing the conditional check in a better way?

Answer 1

iif is the only rxjs conditional that could help, but the main issue here is that it only allows for a true or false check. In your case there are more scenarios, so you'd need to chain them.

I think simple boolean logic like you have is fine, although you could simplify your code by removing && newPeople.length === 0 and && peopleToRemove.length === 0 from the else if s. If the if(newPeople.length > 0 && peopleToRemove.length > 0) check is false (reaching the else if s), it's already guarantees one of the array is empty, so checking for the one with length > 0 is enough.

if(newPeople.length > 0 && peopleToRemove.length > 0) {
  return forkJoin([this.eventService.addPeople(res.id, newPeople), this.eventService.removePeople(res.id, peopleToRemove)])
}
//if newPeople isn't empty, then peopleToRemove is guaranteed to be empty
else if(newPeople.length > 0) {
  return this.eventService.addPeople(res.id, newPeople)
}
//if peopleToRemove isn't empty, then newPeople is guaranteed to be empty
else if(peopleToRemove.length > 0) {
  return this.eventService.removePeople(res.id, peopleToRemove)
}