I'm working on getting my site to support the eTag/If-None-Match browser cache, but I'm not sure which browsers do/don't support it. Can anyone point me to a list? I can't imagine it's universal, but I haven't found anything that supports that claim.
cheers,
Mike
If-None-Match was Specified in HTTP 1.1 (June 1999):
According to Wikipedia:
By March 1996, pre-standard HTTP/1.1 was supported in Arena, Netscape 2.0, Netscape Navigator Gold 2.01, Mosaic 2.7, Lynx 2.5, and in Internet Explorer 3.0. End user adoption of the new browsers was rapid. In March 1996, one web hosting company reported that over 40% of browsers in use on the Internet were HTTP 1.1 compliant. That same web hosting company reported that by June 1996, 65% of all browsers accessing their servers were HTTP/1.1 compliant. The HTTP/1.1 standard as defined in RFC 2068 was officially released in January 1997. Improvements and updates to the HTTP/1.1 standard were released under RFC 2616 in June 1999.
In my experience, all browsers in popular use, IE5.5+, Safari, Chrome, Opera, and Firefox, all support the ETag/If-None-Match headers.
However, there are some other headers which will stop these browsers from respecting the etag... so if it's not working for you, I'd carefully examine the other headers being sent back to the client when they request a resource.
Do you have any particular reason for asking the question? Maybe if you had a specific instance you were having an issue with, we could look at the other headers?
But these headers have been around for a long time, and they are a key caching mechanism used widely around the net.
来源：https://stackoverflow.com/questions/6247761/browser-support-for-etags