Simple JavaScript Constants

constant.js

/*
 * JavaScript Constant
 *
 * Create constants via Api
 * Retreive values from window/global without Api
 *
 * This will work in both browsers and node
 *
 * Enforces standard rules:
 *   Requires uppercase naming conventions
 *   Does not allow right hand assignment once constant is set
 */

var global = this;

function constant(name, value) {
  if(!isUppercase(name)) {
    constant._error('Illegal constant name.', name);
  }

  if(isGloballyDefined(name)) {
    constant._error('Constant already defined.', name);
  }

  constant._define(name, value);
}

constant._error = function(msg, name) {
  throw new Error('CONSTANT ERROR: ' + msg  + ' For constant: ' + name);
};

constant._define = function(name, value) {
  Object.defineProperty(global, name, {
    get: function() {
      return value;
    },
    set: function(val) {
      constant._error('Illegal right hand assignment.', name);
    }
  });
};

constant._remove = function(name) {
  if(isGloballyDefined(name)) {
    global[name] = undefined;
  } else {
    constant._error('Cannot delete undefined constant.', name);
  }
};

function isUppercase(value) {
  return value === value.toUpperCase();
}

function isGloballyDefined(value) {
  return !isUndefined(global[value]);
}

function isUndefined(value) {
  return value === undefined;
}

constant('PERSON', 'Tyler');
constant('AGE', 26);

console.log(PERSON);
// => Tyler

console.log(AGE);
// => 26

PERSON = 'Steve';
// => Error: Illegal right hand assignment for constant: PERSON

constant('Person', 'Tyler');
// =>  Illegal constant name - must be uppercase