How does “304 Not Modified” work exactly?

Question

• How are \"304 Not Modified\" responses generated?

• How does a browser determine whether the response to an HTTP request is 304?

• Is it

Answer 1

Last-Modified : The last modified date for the requested object

If-Modified-Since :　Allows a 304 Not Modified to be returned if last modified date is unchanged.

ETag : An ETag is an opaque identifier assigned by a web server to a specific version of a resource found at a URL. If the resource representation at that URL ever changes, a new and different ETag is assigned.

If-None-Match : Allows a 304 Not Modified to be returned if ETag is unchanged.

the browser store cache with a date(Last-Modified) or id(ETag), when you need to request the URL again, the browser send request message with the header:

the server will return 304 when the if statement is False, and browser will use cache.