constants.js

var constant= (function() {
  var allowed = {
      string: true,
      number: true,
      boolean: true
    },
    ownProp = Object.prototype.hasOwnProperty,
    constants = {},
    prefix,
    isDefined;

  prefix = (Math.random() + '_').slice(2);

  isDefined = function(name) {
    return ownProp.call(constants, prefix + name);
  };

  return {
    set: function(name, value) {
      if(isDefined(name)) {
        return false;
      }

      if(!ownProp.call(allowed, typeof value)) {
        return false;
      }

      constants[prefix + name] = value;
      return true;
    },

    get: function() {
      if(isDefined(name)) {
        return constants[prefix + name];
      }

      return null;
    },

    all: function() {
      return constants
    }
  }
} ());

constant.set('hue', 123); // true
constant.get('hue'); // 123
constant.set('hue', 456); // false
constant.get('hue'); // 123

constant.set('notAllowed', {}); // false
constant.get('notAllowed'); // null