1.失败

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();});

　　

2.失败

if (req.method === 'OPTIONS') {      console.log('!OPTIONS');      var headers = {};      // IE8 does not allow domains to be specified, just the *      // headers["Access-Control-Allow-Origin"] = req.headers.origin;      headers["Access-Control-Allow-Origin"] = "*";      headers["Access-Control-Allow-Methods"] = "POST, GET, PUT, DELETE, OPTIONS";      headers["Access-Control-Allow-Credentials"] = false;      headers["Access-Control-Max-Age"] = '86400'; // 24 hours      headers["Access-Control-Allow-Headers"] = "X-Requested-With, X-HTTP-Method-Override, Content-Type, Accept";      res.writeHead(200, headers);      res.end();} else {//...other requests}

　　

3. app.all('*', function (req, res, next) {    res.header("Access-Control-Allow-Origin", "*");    res.header("Access-Control-Allow-Methods", "PUT,POST,GET,DELETE,OPTIONS");    res.header("Access-Control-Allow-Credentials", false);    res.header("Access-Control-Max-Age", '86400');    res.header("Access-Control-Allow-Headers", "X-Requested-With, X-HTTP-Method-Override, Content-Type, Accept");    res.header("Content-Type", "application/json;charset=utf-8");    res.header("X-Powered-By", ' 3.2.1');    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...