Crossing the Site Domain with JavaScript
Browsers try to prevent a range of malicious attacks by preventing content being accessed by a web page from a different domain to the one that the page was fetched from. If you have a legitimate need to do this, it is a bad idea to disable this method of defence: Instead, there are more legitimate and safer ways of performing cross-domain JavaScript calls such as JSONP or Cross-Origin Resource Sharing, as Dino explains.