Convert numbers to base 64

base-64-numbers.js

(function() {

const BASE_64_CHARS = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz+/'.split('');

Number.prototype._toString = Number.prototype.toString;
window._parseInt = window.parseInt;

Number.prototype.toString = function(base) {
  if (base < 37 && base >= 2) {
    return Number.prototype._toString.call(this, ...arguments);
  }
  
  base = Math.trunc(base);
  if (base > 64 || base < 2) {
    throw 'Uncaught RangeError: toString() radix argument must be between 2 and 64';
  }

  let base64Chars = BASE_64_CHARS.slice(0, base);
  let rest = Number(this) || 0;
  let base64 = '';
  while (true) {
    rest = Math.floor(rest);
    base64 = base64Chars[rest % base] + base64;
    if (rest < base) {
      break;
    } else {
      rest = rest /= base;
    }
  }
  return base64;
};

window.parseInt = function(str, base) {
  if (base < 37) {
    return window._parseInt(...arguments);
  }
  
  base = Math.trunc(base);
  if (base > 64) {
    return NaN;
  }

  let base64Chars = BASE_64_CHARS.slice(0, base);
  let chars = String(str).split('');
  let decimal = 0;
  for (let [i, char] of Object.entries(chars)) {
    let position = base64Chars.indexOf(char);
    if (position === -1) { return NaN; }
    decimal += position * Math.pow(base, chars.length - Number(i) - 1);
  }
  return decimal;
}

})();