why new Date add 1 day js code example

Example 1: js date add 1 day

let date = new Date();
// add a day
date.setDate(date.getDate() + 1);

Example 2: javascript add day to date

function addDays(date, days) {
  var result = new Date(date);
  result.setDate(result.getDate() + days);
  return result;
}