NOTE: This creates GUID-like strings and not GUIDs. @broofa's node-uuid module is much better than this implementation.

In its simplest form, Guid lets you generate raw GUID formatted strings:

Guid.raw();
// -> '6fdf6ffc-ed77-94fa-407e-a7b86ed9e59d'

Let's generate a new Guid instance.

var guid = Guid.create();

We've now got an object which we can work with programmatically. Lets check the validity of our Guid using the built-in validator:

Guid.isGuid(guid);
// -> true

Guid.value;
// -> '6fdf6ffc-ed77-94fa-407e-a7b86ed9e59d'

A handy bit of functionality is that its toString method returns the string value, so you can do handy things like this:

var itemUrl = "http://whatever.com/items/" + guid;
// -> 'http://whatever.com/items/6fdf6ffc-ed77-94fa-407e-a7b86ed9e59d'

If you need a placeholder Guid, or a value to represent a non-GUID, use the static EMPTY property:

Guid.EMPTY;
// -> '00000000-0000-0000-0000-000000000000'

Once you have a Guid object, you can't change its value (thanks ES5!):

guid.value = "go suck it, guid!"
guid.value;
// -> '6fdf6ffc-ed77-94fa-407e-a7b86ed9e59d'

To instantiate an Guid object using an existing GUID string, use the constructor:

var guid = new Guid('6fdf6ffc-ed77-94fa-407e-a7b86ed9e59d');

You can check the equality of two different Guid objects using the equals instance method.

Compare a Guid object to a GUID string:

guid.equals('6fdf6ffc-ed77-94fa-407e-a7b86ed9e59d');
// -> true

Compare two Guid objects:

guid.equals(new Guid('6fdf6ffc-ed77-94fa-407e-a7b86ed9e59d'));
// -> true

You can use npm to install guid: npm install guid

There's also a Uuid library which has the exact same functionality, but for UUID's: https://github.com/dandean/uuid-lib