The introduction of AJAX marked a huge leap forward in the history of the web. The ability to communicate with a web server without reloading the page has revolutionised how web applications are built. The primary technology that enables AJAX (XMLHttpRequests) has evolved significantly since the initial conception of dynamic websites.

A nice feature added to XMLHttpRequests in recent years is the ability to handle file uploads. Traditionally many developers have resorted to using technologies like Flash to upload files to a server. The problem with this approach is that the user needs to have a third-party browser plugin installed.

In this post you’ll learn how to upload files to a server using native JavaScript technologies. The example we’re going to use supports uploading multiple files in a single request. However, you can apply the same principles to single-file uploads too.