(function() {
  'use strict';

  function $(id) {
    return document.getElementById(id);
  }

  //Decimal point works only for base 10(decimal) number!
  function baseConverter(str, fromBase, toBase) {
    str = /\./.test(str) ? +str : parseInt(str, fromBase);
    return str.toString(toBase);
  }

  var form = $('form');

  form.onchange = function() {
    form.out_data.value = baseConverter(form.input_data.value,
      form.fromBase.value,
      form.toBase.value);
  };

}());