nodejs 解决跨域

app.all('*', function (req, res, next) {
    res.header("Access-Control-Allow-Origin", "*");
    res.header("Access-Control-Allow-Headers", "X-Requested-With");
    res.header("Access-Control-Allow-Methods", "PUT,POST,GET,DELETE,OPTIONS");
    res.header("X-Powered-By", ' 3.2.1');
    res.header("Content-Type", "application/json;charset=utf-8");
    next();
});

　　

“简单请求”
 请求方法是以下三种方法之一：
HEAD
GET
POST

“非简单请求”
HTTP的头信息不超出以下几种字段：
Accept
Accept-Language
Content-Language
Last-Event-ID
Content-Type：
application/x-www-form-urlencoded、 multipart/form-data、text/plain
不满足这些特征的请求称为“非简单请求”，例如：content-type=applicaiton/json , method = PUT/DELETE...