Javascript Convert Date Time string to Epoch

var someDate = new Date(dateString);
someDate = someDate.getTime();

You can use Date.parse(date).

function epoch (date) {
  return Date.parse(date)
}

const dateToday = new Date() // Mon Jun 08 2020 16:47:55 GMT+0800 (China Standard Time)
const timestamp = epoch(dateToday)

console.log(timestamp) // => 1591606075000