Zumber, weird numbers.

Zumber.js

-function() {
  function Zumber(array) {
    if(!(this instanceof Zumber))
      return new Zumber(array);

    if(!(
      array instanceof Array &&
      array.length > 10 &&
      array.every(function(item, index) {
        return typeof(item) === 'string' && item.length === 1 && !~array.indexOf(item, index + 1);
      })
    )) throw Error('The first argument must be an array of one-character-strings and each string must be unique in that array.', 1);

    Object.defineProperties(this, {
      _base: {value: array, writable: false, configurable: false},
      _base_flipped: {
        writable: false, configurable: false, value: array.reduce(function(_base_flipped, character, index) {
          _base_flipped[character] = index;
          return _base_flipped;
        }, {})
      }
    });
  }

  Object.defineProperties(Zumber.prototype, {
    encode: {
      writable: false, configurable: false, value: function(number) {
        if(~~number !== number) return false;
        var sign = number < 0 ? '-' : '';
        var positive_number = Math.abs(number);

        if(positive_number < this._base.length)
          return sign + this._base[positive_number];

        var zumber = [];
        var rest = positive_number;

        do {
          rest = positive_number / this._base.length | 0;
          zumber = this._base[positive_number % this._base.length] + zumber;
          positive_number = rest;
        } while(rest >= this._base.length);

        zumber = this._base[rest] + zumber;
        return sign + zumber;
      }
    },
    decode: {
      writable: false, configurable: false, value: function(zumber) {
        if(!this.isValidZumber(zumber)) return false;
        var _self = this;
        var sign = '';
        if(zumber[0] === '-') {
          sign = '-';
          zumber = zumber.substr(1);
        }
        return +(sign + zumber.split('').reduce(function(number, zumber) {
          number.unshift(_self._base_flipped[zumber]);
          return number
        }, []).reduce(function(result, number, index) {
          return result + number * Math.pow(_self._base.length, index);
        }, 0));
      }
    },
    isValidZumber: {
      writable: false, configurable: false, value: function(zumber) {
        var _self = this;
        return typeof(zumber) === 'string' && zumber.split('').every(function(zumber, index) {
          return ~_self._base.indexOf(zumber) || (index === 0 && zumber === '-');
        });
      }
    }
  });

  if(typeof module === 'object' && typeof module.exports === 'object')
    module.exports = Zumber;
  else if(typeof window === 'object')
    window.Zumber = Zumber;
  else
    throw new Error('I don\'t know how to export this')
}()