javascript-algorithms/src/algorithms/math/bits/bitLength.js

/**
 * Return the number of bits used in the binary representation of the number.
 *
 * @param {number} number
 * @return {number}
 */
export default function bitLength(number) {
  let bitsCounter = 0;

  while ((1 << bitsCounter) <= number) {
    bitsCounter += 1;
  }

  return bitsCounter;
}