"Ajax Principles Detailed Video Tutorial" The core of Ajax is the XMLHttpRequest object, referred to as XHR. It is used to enable the browser to request additional data from the server without unloading the page, which greatly improves the user experience. Prior to this, this technology actually existed and was implemented by some people, but it was not popular and was not supported by browsers. However, after that, IE5 introduced XHR objects for the first time and supported ajax technology, which was subsequently supported by all browsers.