C's math.frexp in JavaScript

module.exports = functionfrexp (arg) {
//  discuss at: https://locutus.io/c/frexp/
// original by: Oskar Larsson Högfeldt (https://oskar-lh.name/)
//      note 1: Instead of
//      note 1: double frexp( double arg, int* exp );
//      note 1: this is built as
//      note 1: [double, int] frexp( double arg );
//      note 1: due to the lack of pointers in JavaScript.
//      note 1: See code comments for further information.
//   example 1: frexp(1)
//   returns 1: [0.5, 1]
//   example 2: frexp(1.5)
//   returns 2: [0.75, 1]
//   example 3: frexp(3 * Math.pow(2, 500))
//   returns 3: [0.75, 502]
//   example 4: frexp(-4)
//   returns 4: [-0.5, 3]
//   example 5: frexp(Number.MAX_VALUE)
//   returns 5: [0.9999999999999999, 1024]
//   example 6: frexp(Number.MIN_VALUE)
//   returns 6: [0.5, -1073]
//   example 7: frexp(-Infinity)
//   returns 7: [-Infinity, 0]
//   example 8: frexp(-0)
//   returns 8: [-0, 0]
//   example 9: frexp(NaN)
//   returns 9: [NaN, 0]
// Potential issue with this implementation:
// the precisions of Math.pow and the ** operator are undefined in the ECMAScript standard,
// however, sane implementations should give the same results for Math.pow(2, <integer>) operations
// Like frexp of C and std::frexp of C++,
// but returns an array instead of using a pointer argument for passing the exponent result.
// Object.is(n, frexp(n)[0] * 2 ** frexp(n)[1]) for all number values of n except when Math.isFinite(n) && Math.abs(n) > 2**1023
// Object.is(n, (2 * frexp(n)[0]) * 2 ** (frexp(n)[1] - 1)) for all number values of n
// Object.is(n, frexp(n)[0]) for these values of n: 0, -0, NaN, Infinity, -Infinity
// Math.abs(frexp(n)[0]) is >= 0.5 and < 1.0 for any other number-type value of n
// See https://en.cppreference.com/w/c/numeric/math/frexp for a more detailed description
  arg = Number(arg)
const result = [arg, 0]
if (arg !== 0 && Number.isFinite(arg)) {
const absArg = Math.abs(arg)
// Math.log2 was introduced in ES2015, use it when available
const log2 = Math.log2 || functionlog2 (n) { returnMath.log(n) * Math.LOG2E }
let exp = Math.max(-1023, Math.floor(log2(absArg)) + 1)
let x = absArg * Math.pow(2, -exp)
// These while loops compensate for rounding errors that sometimes occur because of ECMAScript's Math.log2's undefined precision
// and also works around the issue of Math.pow(2, -exp) === Infinity when exp <= -1024
while (x < 0.5) {
      x *= 2
      exp--
    }
while (x >= 1) {
      x *= 0.5
      exp++
    }
if (arg < 0) {
      x = -x
    }
    result[0] = x
    result[1] = exp
  }
return result
}