date.js

function date(date = new Date(), props = {}) {
  [date, props] =
    date.constructor.name === "Object"
      ? [new Date(), date]
      : [new Date(date), props];

  for (let key in props) {
    if (typeof props[key] === "string" && props[key].match(/^[+-]/))
      props[key] = date[key.replace(/^set/, "get")]() + parseInt(props[key]);
    date[key](props[key]);
  }
  return date;
}

/* USAGE:

  date('2022-09-18')
  date(new Date('2022-09-17'))
  date('2022-09-19', { setDate: '-1' })
  date('2022-09-19', { setDate: 25 })
  date({ setDate: '-1' })
  date()

*/