Node 心中有坑，处处是坑

V2EX = way to explore

V2EX 是一个关于分享和探索的地方

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这是一个创建于 2675 天前的主题，其中的信息可能已经有所发展或是发生改变。

记录一个 Node 的坑

新手接触 Node 不到一个月，遇到了很多坑

后端代码是这样写的：

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");
	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();
});

然而前端每次发送 AJAX 跨域请求时都收不到结果，错误信息为网关超时

 XMLHttpRequest cannot load http://111.111.111.111:8089/login_service. Response to
 preflight request doesn't pass access control check: No
 'Access-Control-Allow-Origin' header is present on the requested resource. Origin
 'http://111.111.111.111' is therefore not allowed access. The response had HTTP
 status code 504.

后来发现前端使用 CORS 请求时content-type取值为application/json; charset=utf-8，也就是说发送跨域请求时会发送 OPTIONS 预检请求，而我没有对设置 OPTIONS 路由，因此成功入坑。后来把后端代码改为了

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') {
	   console.log('you can do that!!');
	   res.send(200); // 让 options 请求快速返回
	} else {
		next();
	}
});