Request header field Content-Type is not allowed by Access-Con

后台设置

app.all('*', function (req, res, next) {    
    res.header("Access-Control-Allow-Origin", "*");
    res.header("Access-Control-Allow-Headers", "X-Requested-With, Content-Type");
    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();
});

之前没设置content-type，一直报

Request header field Content-Type is not allowed by Access-Control-Allow-Headers

的错