Recently I've worked on the application making cross-domain ajax calls with YUI . While YUI offers io-xdr module for making cross-domain requests via Flash transport , it seems to me quite unnatural as it leads to unnecessary complexity. Moreover, io-xdr was marked deprecated several months ago without explicit mentioning the preferred way. An obvious alternative is using XMLHttpRequest as a transport for cross-domain requests. However, it has some limitations and undocumented pitfalls that I'd like to review in this post. Cross-Domain request using XMLHttpRequest. YUI IO Utility. YUI Datasource IO. Cross-Domain request using XMLHttpRequest Cross-domain requests can be sent using a common XMLHttpRequest object. The only requirement is that the server must be configured to properly handle those requests. Specifically, it should set the Access-Control-Allow-Origin response header according to Cross-Origin Resource Sharing specification . For more details and good tuto