Understanding JavaScript's Single-Threaded Execution and the Role of Web Workers

JavaScript runs one thing at a time because it’s single-threaded. This is simpler for programmers because you don’t have to worry about multiple things happening at once. For example, when you’re working on a document, you can be sure that no one else is messing with it at the same time. So you don’t have to worry about things like locks and race conditions, which are situations where things go wrong because multiple things are happening at once.

Being single-threaded means that the web browser stops doing anything else while it’s running JavaScript code. So, if you write code that takes a long time to run, it could slow down the loading of the web page, or make the browser unresponsive, which could frustrate the user.

To help with this, web developers can use something called a “web worker”. This is like a helper that can do hard work in the background without slowing down the user interface. However, a web worker can’t touch the document content and doesn’t share anything with the main JavaScript program or other workers. It can only talk to them by sending and receiving messages. This way, the main JavaScript program can continue doing its thing without any interruptions.

Two event handlers cannot run at the same time. Only one thread can modify the DOM at a time. So there is no need to worry about locks, deadlock or race conditions when writing JavaScript code. A web worker is a background thread for performing computationally intestive tasks without freezing the user interface. The code that runs in a web worker thread does not have access to document content, does not share any state with the main thread or with other workers. It can only communicate with the main thread and other workers through asynchronous message events, so the concurrency is not detectable to the main thread. Web workers do not alter the basic single-threaded execution model of JavaScript programs.