Although the XMLHttpRequest object is not yet an official W3C standard, leading web browsers have implemented comparable functionality. Unfortunately, the lack of a unified specification resulted in a little extra work for developers.

Microsoft was the first to implement an XMLHTTP object in their web browser as an ActiveX component. The Mozilla Organization followed suit and built a comparable XMLHttpRequest object into the XML Extras module, which is shipped with most gecko-based browsers. Rarely do developers know which browser their clients will use. Therefore, to utilize Ajax, developers are required to write code specific to each platform, resulting in browser detection code and multiple blocks of code with overlapping functionality.