26. What are Web Workers?

Web Workers helps us to run javascript code in the background without blocking application.
Web Workers runs in an isolated (new) thread for executing our javascript code.
Web Workers are usually used for large tasks.
Web Workers needs a seperate file for our javascript code.
Web Workers files are downloaded asynchronously.
Web Workers are supported in all latest browser.

Example:

Our client side js file below:

var myWebWorker = new Worker("task.js"); // Creating a worker

// Listen to task.js worker messages
worker.addEventListener("message", function(event) {
  console.log("Worker said: ", event.data);
}, false);

worker.postMessage("From web worker file"); // Will start the worker

task.js (worker file) file below:

// Listen to client js file post messages
self.addEventListener("message", function(event) {
  self.postMessage(event.data); // Send processed data to listening client js file.
}, false);

More on Web Workers.