Merge different Array variables value into JSON Object

I have below respective variables holding the bill# in an array.

billA = [12345]  // For "Pizzahut" Billsystem 

billB = [96754,75432]  // For "Subway" Billsystem

billC = [63946]   // For "XYZ" Billsystem

I intend to combine the above values into a JSON object like the below format.

Result Output:

{"BillDetails" : [{billsystem: "PizzaHut" , billnum: "12345"}, {billsystem : "Subway" , billnum "96754" }, {billsystem : "Subway" , billnum "75432"},{billsystem : "XYZ" , billnum "63946"}]}

>Solution :

You could use flatMap along with an array of billing systems

let billA = [12345] // For "Pizzahut" Billsystem 
let billB = [96754, 75432] // For "Subway" Billsystem
let billC = [63946] // For "XYZ" Billsystem
let billD = [] // For "Testing" Billsystem
let types = ["Pizzahut", "Subway", "XYZ", "Testing"]
let json = {
  BillDetails: [billA, billB, billC, billD].flatMap((e, i) => (e?.map(b => ({
    billSystem: types[i],
    billNum: b
  }))))
}

console.log(json)