为什么 XML 会成为 MEAN 堆栈应用程序的问题，这个错误是关于什么的？

Question

I am currently working on a socket.io "hello world" via a MEAN stack application, and right away Chrome is tossing some funky errors my way. To be honest, in the debugging effort, I'm not sure even where to begin. My initial questions were:

• Why is XML being used instead of JSON?
• What does No 'Access-Control-Allow-Origin' header is present on the requested resource. even mean?

The entire error message is below, and thanks in advance for any advice y'all are able to give.

Cheers,

Peter

XMLHttpRequest cannot load http://localhost/socket.io/?EIO=3&transport=polling&t=1435600202687-6. No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:9000' is therefore not allowed access. The response had HTTP status code 404.

Answer 1

Try including the socket.io lib directly from the socket server:

<script src="http://localhost:9000/socket.io/socket.io.js"></script>

The Error "No 'Access-Control-Allow-Origin' header is present on the requested resource." means that your server doesn't allow an extern resource to connect.

Additionally you can set the allowed origins directly in the io setup eg:

var io = require('socket.io')(server, {origins:'page.com:* http://page.com:* http://www.page.com:*'});