Communicating with a server.
WHAT A REQUEST INVOLVES
An address A method, indicating intent Headers Sometimes a body
WHAT TO ALWAYS CHECK
The response status, before using the content.
WHY
A failed request still returns a response, and treating it as data produces confusing errors.
WHAT FORMAT IS USUALLY USED
Structured text, parsed into objects.
WHAT TO VALIDATE
That the response has the shape you expect.
WHY
External data changes, and assuming its structure produces failures in production.
WHAT TO HANDLE
Network failure Unexpected status codes Responses in the wrong format Slow responses
WHAT TO NEVER PUT IN BROWSER CODE
Secrets of any kind.
WHY
Everything in the browser is visible to the user.
WHAT THAT MEANS
Any key in your JavaScript is public.
WHAT TO DO INSTEAD
Route requests requiring secrets through your own server.
WHAT TO BE AWARE OF
Cross-origin restrictions, which prevent a page reading responses from other sites unless permitted.
WHY THEY EXIST
To prevent one site reading your data from another.
