Rounding with precision

round-prec.js

// Arrow functions
const round = (num, prec) => (prec = 10 ** prec, Math.round(num * prec) / prec);
const roundUp = (num, prec) => (prec = 10 ** prec, Math.ceil(num * prec) / prec);
const roundDown = (num, prec) => (prec = 10 ** prec, Math.floor(num * prec) / prec);

// Classic functions
function round(num, prec) {
  prec = Math.pow(10, prec);
  return Math.round(num * prec) / prec;
}
function roundUp(num, prec) {
  prec = Math.pow(10, prec);
  return Math.ceil(num * prec) / prec;
}
function roundDown(num, prec) {
  prec = Math.pow(10, prec);
  return Math.floor(num * prec) / prec;
}