One of the main contributors to the language and it's use evolving is AJAX. Those four letters took the idea that a webpage was a single piece of content and turned it on it's head allowing programmers to bring in new content to the page. The first letter is perhaps the most important, asynchronous.
Being asynchronous the sites could change and become a whole new page without ever navigating, new content could be brought in and so we could do more with the page that we were on. This also meant that we could process the information that was sent to us and move the logic from the server side to the client side. Because of this we needed two new advances.
The first was how to send the information. The last letter stood for XML. This was a cumbersome way of giving data which was tricky to traverse and had a lot of repetition. Luckily there was a data format that we were already familiar with JSON.