What's the difference between Shared Worker and Worker in HTML5?

Very basic distinction: a Worker can only be accessed from the script that created it, a SharedWorker can be accessed by any script that comes from the same domain.

SharedWorker's seem to have more functionality then Worker.

Among that functionality is :

• A shared global scope. All SharedWorker instances share a single global scope.

W3C Spec:

• SharedWorker
• Worker

WHATWG Spec:

• SharedWorker
• Worker

To anyone considering using SharedWorker -- Apple removed support of SharedWorker from WebKit in 2015. In their current roadmap there is no plan for reimplementation. Support for Service Workers is currently under development for WebKit and offer similar capabilities (see here for comparisons).

You can follow the development (aka Safari support) of ServiceWorkers in WebKit here.