baseConversion.js

/**
 * range of available symbols for maximum radix (i.e. 61)
 * @type {string}
 */
const range = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";

/**
 * converts JavaScript number from other bases to decimal
 *
 * @param {number} value number to be converted
 * @param {number} sourceBase base of first param
 * @returns {number} first param in decimal
 */
const convertToDecimal = (value, sourceBase) =>
  String(value)
    .split("")
    .reverse()
    .reduce((sum, num, index) => {
      const decimal = range.indexOf(num) * sourceBase ** index;
      return sum + decimal;
    }, 0);

/**
 * converts JavaScript number from decimal to other bases
 *
 * @param {number} decimalValue number to be converted
 * @param {number} targetBase base of the return value
 * @returns {number} first param in target base
 *
 */
const convertFromDecimal = (decimalValue, targetBase) => {
  let result = "";
  while (decimalValue > 0) {
    result = range[decimalValue % targetBase] + result;
    decimalValue = Math.floor(decimalValue / targetBase);
  }
  return result;
};

/**
 * converts JavaScript number from and to any bases (read max radix in 1st line)
 *
 * @param {number} value number to be converted
 * @param {number} sourceBase base of first param *
 * @param {number} targetBase base of the return value
 * @returns {number} first param in target base
 * @example convertBase(255, 10, 16)
 * //=> "ff"
 */
const convertBase = (value, sourceBase, targetBase) => {
  let decimalValue;
  if (sourceBase === 10) {
    decimalValue = value;
  } else {
    decimalValue = convertToDecimal(value, sourceBase);
  }

  if (targetBase === 10) return decimalValue;

  return convertFromDecimal(decimalValue, targetBase);
};