如何使用JavaScript捕获缓存清除事件？

Question

I am working on a socket based chat project. I am storing all online users' name in database so that it can be checked for duplicate user name. My application makes user offline easily if we are chatting and we directly close our browser but the problem is that when we directly clear cache memory at that time that AJAX call for deleting user from database will not be called. So even if we have cleared the cache and became offline, we are displayed online to the front user meaning that the entry still persist in data base because no AJAX call was fired and we had directly cleared cache.

So, anybody who has some idea regarding how to catch cache clear event using javascript , please let me know.

I have done a lot of googling on this issue but nothing found.

Any suggestion will be entertained.

Thnx in advance.....

Answer 1

What you are asking for is impossible (there is no way to detect when the user clears their browser cache from JavaScript).

Have you considered sending an invisible "ping" between both users every so often (pick a threshold like 1 minute), and for both users if they don't receive a ping for (threshold + smaller threshold), will consider the other user to be offline (or more robustly send a request for another "I am still here" ping).