nodejsexpressNo_AccessControlAllowOrigin_header_is_present_on_the_requested_resou_0">零基础解决node.js+express服务跨域问题，No ‘Access-Control-Allow-Origin’ header is present on the requested resou

前端-vue跨域

这里说明一下，网上很多都是潦草的说什么方法，具体根本自己就不会解决，
写那么多博客一模一样有什么意思，又不能解决问题，看到我就想小嘴抹蜜。

• 出现的问题：

Access to XMLHttpRequest at 'http://localhost:3000/user/login' from origin 'http://localhost:8080' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.

• 解决办法

  在服务器的app.js引入下面这段代码

注意：一定要在app.use()之前引入

• 代码

//设置跨域访问
app.all('*', function(req, res, next){
  res.header('Access-Control-Allow-Origin',  '*');
  res.header('Access-Control-Allow-Headers', 'Content-Type, Content-Length, Authorization, Accept, X-Requested-With, yourHeaderFeild');
  res.header('Access-Control-Allow-Methods', 'PUT, POST, GET, DELETE, OPTIONS');
  if (req.method === 'OPTIONS'){
    res.sendStatus(200);
  }else{
    next();
  }
});