guid.js

(function () {
  var validator = new RegExp("^[a-z0-9]{8}-[a-z0-9]{4}-[a-z0-9]{4}-[a-z0-9]{4}-[a-z0-9]{12}$", "i");

  function gen(count) {
    var out = "";
    for (var i=0; i<count; i++) {
      out += (((1+Math.random())*0x10000)|0).toString(16).substring(1);
    }
    return out;
  }

  function Guid(guid) {
    if (!guid) throw new TypeError("Invalid argument; `value` has no value.");
      
    this.value = Guid.EMPTY;
    
    if (guid && guid instanceof Guid) {
      this.value = guid.toString();

    } else if (guid && Object.prototype.toString.call(guid) === "[object String]" && Guid.isGuid(guid)) {
      this.value = guid;
    }
    
    this.equals = function(other) {
      // Comparing string `value` against provided `guid` will auto-call
      // toString on `guid` for comparison
      return Guid.isGuid(other) && this.value == other;
    };

    this.isEmpty = function() {
      return this.value === Guid.EMPTY;
    };
    
    this.toString = function() {
      return this.value;
    };
    
    this.toJSON = function() {
      return this.value;
    };
  };

  Guid.EMPTY = "00000000-0000-0000-0000-000000000000";

  Guid.isGuid = function(value) {
    return value && (value instanceof Guid || validator.test(value.toString()));
  };

  Guid.create = function() {
    return new Guid([gen(2), gen(1), gen(1), gen(1), gen(3)].join("-"));
  };

  Guid.raw = function() {
    return [gen(2), gen(1), gen(1), gen(1), gen(3)].join("-");
  };

  if(typeof module != 'undefined' && module.exports) {
    module.exports = Guid;
  }
  else if (typeof window != 'undefined') {
    window.Guid = Guid;
  }
})();