…Jesse James Garett of Adaptive Path finally gave this use of Javascript a name. He called it Asynchronous Javascript and XML (thankfully shortened to Ajax). Ajax wasn’t a single method or technology, but a group of principles based on the work being done at Google that described how to handle JavaScript in more demanding web applications. The short version is actually fairly simple. Use XMLHttpRequest to make request to the server, take the XML data returned, and lay it out on the page using JavaScript and semantic HTML.
Ajax took off after that. It underpins major parts of modern web development, and has spawned a number of frameworks and methodologies. The technology itself has been swapped out over time. XML was replaced by JSON, and XMLHttpRequest by fetch. That doesn’t matter though. Ajax showed a lot of developers that the web wasn’t just about documents. The web could be used to build applications. That might seem like a small notion, but trust me when I say, it was momentous.
The History of The Web is great, and you should read it, but this piece is particularly interesting. Ajax and its spiritual successors laid the groundwork for rich Internet applications, shell apps, and the real-time Web, but they also paved the way for a handful of the inevitable practices that went alongside: Javascript-required websites, API-driven web and mobile applications with virtually no HTML content whatsoever… and these things have begun to become problematic for the health of the Web as a whole.
I love Ajax, but it absolutely must be employed as progressive enhancement where possible.