Creating an array of objects with random number of properties

May 1, 2022

I am trying to create an array of objects that will be populated by random properties.
I want the objects all to look like this

{ systemStar: "something random", planets: ["random1", "random2", etc]}
Currently I have the following code

const letThereBeLight = () => {
  let universe = []
  const starNumber = 5;
  let randomNumberOfPlanets = Math.floor(Math.random() * 6);
  for (let i = 0; i < starNumber; i++) {
    universe.push({
      systemStar: starList[Math.floor(Math.random() * lengthOfStarList)],
      systemPlanets: [planetList[Math.floor(Math.random() * lengthOfPlanetList)]]
    })

  }

  console.log(universe)
}

This does a great job in creating the objects I want with the following format, however the systemPlanets is only one, instead of a random number. I have tried to do a double for loop but the syntax was eluding me.
How can I get an array of random strings inside of my for loop?

Added variables for clarity

let starList = [
  "Red-Giant",
  "Red-Supergiant",
  "Blue-Giant",
  "White-Dwarf",
  "Yellow-Dwarf",
  "Red-Dwarf",
  "Brown-Dwarf",
];
let planetList = [
  "Rocky",
  "Temperate",
  "Ocean",
  "Frozen",
  "Lava",
  "Gas"
];

>Solution :

Try using Array.from({length:5}) to create an array of 5 elements.
and replace 5 with a random number by using Math.random() * 5 Math.floor() method to round it down to near number, add add one to at least create one planet. then map them to values in source array `planetList.

let starList = [
  "Red-Giant",
  "Red-Supergiant",
  "Blue-Giant",
  "White-Dwarf",
  "Yellow-Dwarf",
  "Red-Dwarf",
  "Brown-Dwarf",
];
let planetList = [
  "Rocky",
  "Temperate",
  "Ocean",
  "Frozen",
  "Lava",
  "Gas"
];
let lengthOfStarList = starList.length;
let lengthOfPlanetList = planetList.length;
let universe = []
const starNumber = 5;
for (let i = 0; i < starNumber; i++) {
    universe.push({
      systemStar: starList[Math.floor(Math.random() * lengthOfStarList)],
      systemPlanets: Array.from({length:Math.floor(Math.random() * 5)+1}).map(x=>planetList[Math.floor(Math.random() * lengthOfPlanetList)])
    })
}
console.log(universe)