(CORS) How does the browser know when to make a request before flying

Question

So, I have been using CORS for a short time, I just read how it works behind the scenes.

My question is: how does the browser know when to make a request before flying?

There is no problem right now, as the browser seems to be working fine, I'm just a little curious. Because when I make a request, I do not give him any information about whether he is CORS, but he still knows what to do before the flight.

Answer 1

The browser will send a request before the flight if:

• You add custom headers to your query
• You are using a method other than GET, HEAD or POST
• You are using POST with an unusual type of content.

: HTTP (CORS),