Asynchronous Code in JavaScript before and after V8 Engine and Node?

I have an assignment where I should learn and write about the history of JavaScript, how the language has started and how it developed to what it is today.

JavaScript is a single threaded language, so blocking by nature. I’m wondering at what point, asynchronous code became possible in JavaScript.

One important point in the history was the release of the V8 engine. It introduced the Event Loop, which allowed for asynchronous Callbacks using the WebApis of the browser. (For example for making Ajax Requests).

But to my knowledge AJAX is quite a bit older then V8, and it was used for making HTTP Requests on the client and updating a webpage asynchronously. So my question is: was asynchronous programming possible before V8? If yes, how was it done and why is V8 considered the beginning of asynchronous programing? If no, was there absolutely no asynchronous code possible before and what was AJAX used for?

Also I would be thankful for other events that marked revolutionary changes in JavaScript. (Besides the different ECMAScript versions).

No, that’s just how JS engines work, just in general.

JS is single threaded, it has to use async programming techniques (via callbacks) otherwise the engine would lock up every time you need to do anything that takes time (there are other ways to deal with this problem – for example Lua uses coroutines, but designer/s of JavaScript chose this method). And to allow that the engine needs a way to deal with them (the event loop).

The APIs that allow for AJAX (XMLHttpRequest and it’s predecessors) was developed by Microsoft in the late 90s (used in IE5 afaik). It’s a collection of browser APIs, it doesn’t really have anything to do with the engine, which just executes JavaScript.

V8 is just a JavaScript engine, the Chromium project’s engine. In many respects it’s very fast compared to predecessors, but it’s notable because Chrome and Node and various other technologies are built in it, not because it’s introduced any JS features (that’s not the point of it – it interprets, compiles and executes JS, it doesn’t add features)

Yes, that’s how JS works, and it worked the same way it does now.

AJAX as a name for that collection of techniques/APIs was coined in the early 2000s, GMail is generally seen as the first massively popular application of it (there were lots before that, just not as popular or influential).