header is present on the requested resource. Origin 'null' is therefore not allowed access.

No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'null' is therefore not allowed access.解决方案

1，如果请求的url是PHP页面，则需要在PHP页面中添加代码：header("Access-Control-Allow-Origin: *");

2，如果请求的url是静态的html页面，则需要在页面中添加meta标签代码：<meta http-equiv="Access-Control-Allow-Origin" content="*" />

3，如果服务器端可以确定是要被哪些域名访问，最好是能把以上代码中的“*”代替为具体的域名，这样做可以相应的增强安全性。

4，最终代码与请求数据如下

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