const arr = ["a", , "b"]
console.log(0 in arr) // true
console.log(1 in arr) // false
console.log(2 in arr) // true
console.log(arr[1]) // undefined

const car = { make: "Honda", model: "Accord", year: 1998 }

console.log("make" in car) // true

delete car.make
if ("make" in car === false) {
  car.make = "Suzuki"
}

console.log(car.make) //Suzuki