try to get a fraction of a number

fraction.ts

// fraction gets up/down from a number
function fraction(v: number, { precise = 5, tries = 100 }): string {
  const [ul, dl] = [[0, 1], [1, 0]];
  const max = parseInt((v - Math.floor(v)).toString().substring(2));
  let [previous, current] = [NaN];
  let c = v;
  for (let i = 2; i < tries; i++) {
    const n = Math.floor(c);
    const uc = n * ul[i - 1] + ul[i - 2];
    if (Math.abs(ul[i]) > max) {
      break;
    }
    const dc = n * dl[i - 1] + dl[i - 2];
    if (precise && dc.toString().length > precise) {
      break;
    }
    ul[i] = uc;
    dl[i] = dc;
    current = uc / dc;
    if (current === previous || current === v) {
      break;
    }
    previous = current;
    c = 1 / (c - n);
  }

  const i = ul.length - 1;
  if (i < 2) {
    return { u: v, d: 1 };
  }
  return { u: ul[i], d: dl[i] };
}

// const v = 0.35141581; // 5 * Math.PI / 11;
// const precise = 8;
// console.log(
//   fraction(v / Math.PI, { precise }),
//   v.toPrecision(precise),
//   (Math.PI * 6525397 / 58335848).toPrecision(precise),
// );