What is the cross domain issue
cross-domain, javascript
Solution
This is a security restriction that prevents requests being made from one origin to another.
For example, it will prevent an `https://` page hitting an `http://` address because the protocol is different.
It will stop `example.com` calling `another.com` because it is a different domain.
It will stop `www.example.com` calling `subdomain.example.com` because it is a different sub domain.
And it will stop `example.com:80` calling `example.com:8080` because it is a different port.
It is possible to make cross-origin requests either using JSONP (if you trust the server!) or using a CORS request (Cross-Origin Resource Sharing), which both client and server must agree to (I can supply more details if you need it on this).
Problem
If I asked a stupid question here, Please don't laugh at me . I have being heard `Cross Domain Issue` many times, But not really get involved in it in real case. So I searched it in the google. But found many posts are talking about `The cross domain issue when make a ajax call`. Not found even a post to tell about what exactly cross domain issue is, and why the cross domain is not allowed? and more question is if I say the cross domain issue, does it mean I made a wrong ajax request to different domain? Any other cases would cause this issue? Thanks. The posts I read are How do I send a cross-domain POST request via JavaScript? "No 'Access-Control-Allow-Origin' header is present on the requested resource"