base-conversion.js

// kata - https://www.codewars.com/kata/526a569ca578d7e6e300034e/

const Alphabet = {
  BINARY: '01',
  OCTAL: '01234567',
  DECIMAL: '0123456789',
  HEXA_DECIMAL: '0123456789abcdef',
  ALPHA_LOWER: 'abcdefghijklmnopqrstuvwxyz',
  ALPHA_UPPER: 'ABCDEFGHIJKLMNOPQRSTUVWXYZ',
  ALPHA: 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ',
  ALPHA_NUMERIC: '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ',
};

const convert = (input, source, target) => {
  const sourceMap = Object.assign({}, ...Array.from(source).map((c, i) => ({ [c]: i })));
  input = Array.from(input)
    .reverse()
    .map((c, i) => Math.pow(source.length, i) * sourceMap[c])
    .reduce((a, b) => a + b, 0);
  let result = '';
  while (input) {
    result = `${target[input % target.length]}${result}`;
    input = Math.floor(input / target.length);
  }
  return result || target[0];
};

const bin = Alphabet.BINARY,
  oct = Alphabet.OCTAL,
  dec = Alphabet.DECIMAL,
  hex = Alphabet.HEXA_DECIMAL,
  allow = Alphabet.ALPHA_LOWER,
  alup = Alphabet.ALPHA_UPPER,
  alpha = Alphabet.ALPHA,
  alnum = Alphabet.ALPHA_NUMERIC;

console.log(convert('15', dec, bin), '1111', '"15" dec -> bin');
console.log(convert('15', dec, oct), '17', '"15" dec -> oct');
console.log(convert('1010', bin, dec), '10', '"1010" bin -> dec');
console.log(convert('1010', bin, hex), 'a', '"1010" bin -> hex');
console.log(convert('0', dec, alpha), 'a', '"0" dec -> alpha');
console.log(convert('27', dec, allow), 'bb', '"27" dec -> alpha_lower');
console.log(convert('hello', allow, hex), '320048', '"hello" alpha_lower -> hex');
console.log(convert('SAME', alup, alup), 'SAME', '"SAME" alpha_upper -> alpha_upper');