It is likely that you have already used or have heard of AJAX. The ubiquitous example is Google Maps, which certainly wasn’t the first but is arguably the most quoted.
AJAX is a very useful technology but have you ever tried to use it across domains? For example, try to send an AJAX request from www.yoursite1.com to www.yoursite2.com. Does it work? Let me save you some time and tell you the answer is no. It won’t work by design. The Javascript specification considers cross-domain XMLHttpRequests to be a security risk, which it can be.
So, what if you have a legitimate business requirement to do cross-domain Javascript requests? The most important reason I can think of for this requirement is a third-party service, or web systems that are distributed across domains. There are many of these types of instances where cross-domain AJAX would be very valuable.
You could require the browser to download a Java applet, which would immediately alienate some browsers. You could use a Flash solution but again, many people simply won’t take the time to download the applet or plugin. More importantly for tracking services, sending Flash or Java applications to browsers on every request is simply not going to scale.
Enter Asynchronous Javascript Across Domains. How does it work?
- Javascript can dynamically generate or load more Javascript.
- Javascript can be loaded across domains.
Is the light going on yet?
So, we write some Javascript that will dynamically append a script tag