Time-determine how many days are the difference between two times

(1) Determine how many days are the difference between the two times

let oldDay = new Date("2020-12-04 15:34:54").getTime()
let newDay = new Date("2020-12-24 21:15:54").getTime()
let cha = parseInt((newDay - oldDay) / (1000 * 60 * 60 * 24))
console.log(cha) // 20

(2) Judge how many days are different from today

let oldDay = new Date("2020-12-04 15:34:54").getTime()
let now = new Date().getTime()
let cha = parseInt((now - oldDay) / (1000 * 60 * 60 * 24))
console.log(cha)