How to use etags for caching?

Question

Can anyone tell me how to pass etag correctly for this url?

https://www.googleapis.com/youtube/v3/playlistItems?part=snippet,id&playlistId=UUwpy_3CqtfwM7tg2JgQQQyA&maxResults=50&key={API_KEY}.

I was passing like this, but didn't work.

https://www.googleapis.com/youtube/v3/playlistItems?part=snippet,id&playlistId=UUwpy_3CqtfwM7tg2JgQQQyA&maxResults=50&key={API_KEY}&If-None-Match="p4VTdlkQv3HQeTEaXgvLePAydmU/vKZr9jiSytaO7UdTbhKbIrwbX20"

Answer 1

If-None-Match is request header, and not query param. Need set this header in headers of request. https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/setRequestHeader