Is JavaScript Synchronous or Asynchronous?

javascript is synchronous by nature but it has a lot of features like callbacks, promises, async/await which allows you to implement asynchronous event handling in your project... hope you get the point :)

Let's not confuse a language's itself with its features!
JavaScript is synchronous itself but features ways of dealing with functions we don't know when they are going to be called.
JavaScript has always been synchronous and single-threaded! When you are running a JavaScript block of code on a page no other block will be executed on that page at the same time.
JavaScript is synchronous when it comes to execution. Look at the code below:

console.log(x)

let x = 5

This is going to throw an error since x is not defined when we are trying to log it.

Check this image out:

This will help you understand how JavaScript works.

And for more information check this article out:
How JavaScript Timers Work

Javascript can be either asynchronous or synchronous. Javascript is most known for being asynchronous because it can be, while other programming languages are multi-threaded at best. It is a huge advantage over other languages because it's so much faster.