php < - > ajax跨域错误

Question

I am using localhost devlopment.

Request headers:

Host                localhost
If-Modified-Since   Sun, 31 May 2015 10:30:44 GMT
If-None-Match       "2486-5175e33a3f259"
Referer             http://localhost/front-page1/front-page/homepage.html
User-Agent          Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0)  
                    Gecko/20100101 Firefox/38.0

Whatever php page i access from ajax, it says

 SyntaxError: Unexpected end of input
at Object.parse (native)
at n.parseJSON (http://localhost/front-page1/front-page/lib/jquery-2.1.3.min.js:4:5309)
at uc (http://localhost/front-page1/front-page/lib/jquery-2.1.3.min.js:4:7333)
at x (http://localhost/front-page1/front-page/lib/jquery-2.1.3.min.js:4:10747)
at XMLHttpRequest.n.ajaxTransport.k.cors.a.crossDomain.send.b 
(http://localhost/front-page1/front-page/lib/jquery-2.1.3.min.js:4:14577)

I don't understand how it became cross domain. And don't even understand the error. Please help me to solve this issue.

I just formatted my system and used sql scripts which are exported from my old system and all other codes are same.

Please let me know if other data required.

ERROR;

$connection = mysqli_connect(DB_SERVER,DB_USERNAME,DB_PASSWORD,DB_DATABASE) or die('{"message":"Database Error","status":"-1"}');

But this die is not getting executed.