请求跨域解决方法CORS

//express后端配置：app.all('*', function(req, res, next) {
 res.header("Access-Control-Allow-Credentials","true"); //服务端允许携带cookie
 res.header("Access-Control-Allow-Origin", req.headers.origin); //允许的访问域
 res.header("Access-Control-Allow-Headers", "X-Requested-With"); //访问头
 res.header("Access-Control-Allow-Methods","PUT,POST,GET,DELETE,OPTIONS"); //访问方法
 res.header("X-Powered-By",' 3.2.1');
 res.header("Content-Type", "application/json;charset=utf-8"); if (req.method == 'OPTIONS') {
 res.header("Access-Control-Max-Age", 800);
 res.sendStatus(204); //让options请求快速返回. } else {
 next();
 }
});