在采用jquery ajax調用http請求時，發現了一系列問題：
如采用firebug調試API請求（這個API是自己服務器的應用），看到服務器明明返回200狀態，response返回數據也是json格式，但ajax返回的error。
在排除json數據格式不正確的原因之后，發現了ajax error函數返回“networkerror failed to execute ‘send' on ‘xmlhttprequest' failed to load ‘http //“ XMLHttpRequest.status=0，就是沒有初始化。
后來才知道是跨域問題（CORS），因為程序調用的是遠程服務器的API，服務器不允許跨域調用。如果只是簡單的方法，只需要在程序的response添加支持跨域的header添加屬性”Access-Control-Allow-Origin: *“即可。如java 服務器代碼：
yourownvariable.setHeader("Access-Control-Allow-Origin:", "origin url of your site");yourownvariable.setHeader("Access-Control-Allow-Methods", "GET, POST,PUT");如果是配置nginx服務器（如果是其他服務器，可以參考：I want to add CORS support to my server），需要在nginx.conf配置文件添加一下內容：
## Wide-open CORS config for nginx#location / {if ($request_method = 'OPTIONS') {add_header 'Access-Control-Allow-Origin' '*';add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';## Custom headers and headers various browsers *should* be OK with but aren't#add_header 'Access-Control-Allow-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Content-Range,Range';## Tell client that this pre-flight info is valid for 20 days#add_header 'Access-Control-Max-Age' 1728000;add_header 'Content-Type' 'text/plain charset=UTF-8';add_header 'Content-Length' 0;return 204;}if ($request_method = 'POST') {add_header 'Access-Control-Allow-Origin' '*';add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';add_header 'Access-Control-Allow-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Content-Range,Range';add_header 'Access-Control-Expose-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Content-Range,Range';}if ($request_method = 'GET') {add_header 'Access-Control-Allow-Origin' '*';add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';add_header 'Access-Control-Allow-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Content-Range,Range';add_header 'Access-Control-Expose-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Content-Range,Range';}}新聞熱點
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