Failed attempt at toFraction()

Better toFraction Attempt.js

function toFraction(num, opt_precision = 6) {
  if (num === Math.ceil(num)) {
    return [num, 1];
  }

  var diff, gcdHelper,
      mult = num < 0 ? -1 : 1,
      numerator = 1, denominator = 2,
      offset = Math.floor(Math.log10(num = Math.abs(num))) + 1,
      acceptableLoss = Math.pow(10, -opt_precision - 1 - offset),
      divisor = Math.pow(10, offset);

  num /= divisor;

  while (true) {
    diff = numerator / denominator - num;
    if (0 <= diff && diff < acceptableLoss) {
      numerator = numerator * divisor;
      divisor = 1;

      if (numerator >= 1 && denominator >= 1) {
        divisor = numerator;
        gcdHelper = denominator;
        while (gcdHelper) {
          num = divisor;
          divisor = gcdHelper;
          gcdHelper = num % gcdHelper;
        }
      }

      return [mult * numerator / divisor, denominator / divisor];
    }
    if (diff < 0) {
      numerator++;
    }
    denominator++;
  }
}

Failed toFraction Attempt.js

console.loadYourJS({ functions: ['gcd', 'fullNumber'] });

//\\
function toFraction(num, opt_precision=6) {
  if (opt_precision !== ~opt_precision && 1 > opt_precision && opt_precision > 13) {
    throw new Error('Precision must be an integer between 1 and 15');
  }

  let parts = YourJS.fullNumber(num).match(/^(-?)(\d+)(?:\.(\d+))?$/);
  let intPart = +parts[2];
  let fracPart = +parseInt((parts[3] + '0'.repeat(opt_precision)).slice(0, opt_precision), 10);

  if (fracPart) {
    let divisor = Math.pow(10, opt_precision);
    let denom = YourJS.gcd(fracPart, divisor);
    divisor /= denom;
    return [(parts[1] ? -1 : 1) * (divisor * intPart + fracPart / denom), divisor];
  }

  return [intPart, 1];
}

//\\
for (var i = 1; i <= 10; i++) {
  for (var j = 1; j <= 10; j++) {
    var fraction = toFraction(i / j, 15);
    console.log(`${i} ÷ ${j} = ${i/j}; ${fraction[0]/fraction[1]} = ${fraction[0]} ÷ ${fraction[1]}`);
  }
}