Ternary Operator Javascript in Else case Do Nothing

Question

I am making a service call having 3 parameters based on IF condition else setting 5 parameters. Need to use Ternary operator to set 4th parameter. Else do not set anything. Below is the code

if (allow) {
   return forkJoin(param1, param2, param3) // Here i need to set param4 based on other condition
} else {
   return forkJoin(param1, param2, param3, param4, param5)
}

I am trying to set using below

if (allow) {
   return forkJoin(param1, param2, this.vipPerson ? param4 : null, param3)
   // But using ternary operator i cant send NULL if this.vipPerson is False. What to do so that 
   // if vipPerson is TRUE it should be like this
   return forkJoin(param1, param2, param3, param4)
   // Else it should be like this 
   return forkJoin(param1, param2, param3)
}

I cant send NULL. Finding the way to send nothing in case if its False

Answer 1

forkJoin takes array of observables, null is not observable. change it to:-

of(null)

you need to import of from rxjs.

Answer 2

A more declarative way would be to define the two possible observables, then use the iif() operator to run the condition. While it's not exactly ternary, it's as close as any RxJS operator gets.

const basic$ = forkJoin(param1, param2, param3);
const vip$ = forkJoin(param1, param2, param3, param4);

return iif(()=>this.vipPerson, vip$, basic$)

https://www.learnrxjs.io/learn-rxjs/operators/conditional/iif