SUMMARY
Workers allow you to run asynchronous JavaScript that will not block the user interface. This is very useful for complex calculations and data processing that would otherwise take up a lot of time and interfere with the user's ability to use the page. Workers are always given their own execution environment, and can only be communicated with via asynchronous messaging.
Workers can be dedicated, meaning they are associated with a single page, or shared, meaning that any page on the same origin can establish a connection with a single worker.
Service workers are designed to allow web pages to behave like native apps. Service workers are also a type of worker, but they behave more like a network proxy than a separate browser thread. They can behave as a highly customizable network cache, and they also can enable push notifications for progressive web applications.
