index.js

var uid = require('uid');

/**
 * Creates a new Symbol object
 */

function Symbol() {
  // allow usage without `new`
  if (!(this instanceof Symbol)) return new Symbol();

  // create a unique key based on a long uid for this symbol
  var key = this.__key__ = "__symbol__" + uid(32);

  // define a property on Object.prototype, so that whenever a property 
  // with the key we just generated is set on any object, it's automatically
  // marked as non-enumerable. this is technically global, but shouldn't matter
  // since it's unique and non-enumerable
  Object.defineProperty(Object.prototype, key, {
    enumerable: false,
    get: function() {},
    set: setter(key)
  });
}

/**
 * Returns the internal string representation of the Symbol object
 */

Symbol.prototype.toString = function() {
  return this.__key__;
};

/**
 * Disposes the global Object.prototype property associated with this symbol
 */

Symbol.prototype.dispose = function() {
  delete Object.prototype[this.__key__];
};

/**
 * Returns a `set` function. This is so that *only* this closure will be
 * retained in memory. Leaving the actual `Symbol` instance to be eligible
 * for garbage collection.
 */

function setter (key) {
  return function(value) {
    // Store the received value and mark it as non-enumerable
    Object.defineProperty(this, key, {
      enumerable: false,
      configurable: true,
      writable: true,
      value: value
    });
  };
}

module.exports = Symbol;