Optional Chaining

let book = {
  name: "Harry Potter 1",
  weight: {
    version1: {
      value: 550,
      unit: 'g'
    },
  }
}

console.log(book?.weight?.version2?.value);
//690

console.log(book?.weight?.version3?.value);
//undefined
// does not throw an error trying to access an undefined property