Web Workers makes it possible to run a script operation in a background thread separate from the main execution thread of a web application. The advantage of this is that laborious processing can be performed in a separate thread, allowing the main (usually the UI) thread to run without being blocked/slowed down.
Uses of of webworker API:-
A worker is an object created using a constructor (e.g. Worker()) that runs a named JavaScript file — this file contains the code that will run in the worker thread.
In addition to the standard JavaScript set of functions (such as String, Array, Object, JSON, etc.), you can run almost any code you like inside a worker thread. There are some exceptions: for example, you can't directly manipulate the DOM from inside a worker, or use some default methods and properties of the Window object. For information about the code that you can run see worker global context and functions, and supported web APIs below.
Data is sent between workers and the main thread via a system of messages — both sides send their messages using the postMessage() method, and respond to messages via the onmessage event handler (the message is contained within the message event's data property). The data is copied rather than shared.
Workers may in turn spawn new workers, as long as those workers are hosted within the same origin as the parent page.
In addition, workers can make network requests using the fetch() or XMLHttpRequest APIs (although note that the responseXML attribute of XMLHttpRequest will always be null).
