Learn HTTP/Networks (Including CORS & WebSockets)

HTTP - The Hypertext Transfer Protocol (HTTP) is an application protocol for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide Web.

Wikipedia

CORS - Cross-origin resource sharing (CORS) is a mechanism that allows restricted resources (e.g., fonts) on a web page to be requested from another domain outside the domain from which the resource originated.

Wikipedia

WebSockets - WebSocket is a protocol providing full-duplex communication channels over a single TCP connection. The WebSocket protocol was standardized by the IETF as RFC 6455 in 2011, and the WebSocket API in Web IDL is being standardized by the W3C.

Wikipedia

HTTP Specifications
HTTP
HTTP Status Codes
CORS Specifications
CORS
WebSockets