Why is JavaScript single-threaded?

Great question! When we say **JavaScript is single-threaded**, it means that the JavaScript engine executes code using a single call stack — it can only do one thing at a time. There is just one thread of execution, so it processes one piece of code sequentially, from top to bottom. This design simplifies the language and avoids many complex issues related to multi-threading, such as race conditions and deadlocks. However, modern web applications often need to handle multiple tasks concurrently, like fetching data from a server, updating the UI, or responding to user input. Browsers handle this by using **asynchronous APIs and an event loop**. While JavaScript itself runs on a single thread, the browser provides other threads behind the scenes for tasks like network requests, timers, and rendering. Here’s how it works in brief: - When you make an asynchronous call (like `fetch` or `setTimeout`), the browser delegates these tasks to other threads. - Once those tasks complete, they queue callback functions into the **event queue**. - The JavaScript engine’s **event loop** continuously checks if the call stack is empty. When it is, it takes the next callback from the event queue and pushes it onto the stack for execution. This event-driven model allows JavaScript to handle concurrent operations efficiently without blocking the main thread, giving the illusion of multitasking while still being fundamentally single-threaded. In summary: **JavaScript is single-threaded in its execution model**, but browsers manage concurrency through asynchronous APIs and the event loop, enabling smooth, non-blocking interactions.