用户关闭浏览器窗口时发送ajax [重复]

Question

This question already has an answer here:

• JavaScript, browsers, window close - send an AJAX request or run a script on window closing 7 answers

My Main GOAL and actual scenario: If two users share the same credentials, then the second user can not login into the system until the first one who is already logged in, log outs system.

Actually I want to set login_flag=0 on server database, when user closes the browser window. I googled and figured out to send an ajax request before either by

$(window).on('unload', function(){ // ajax here with async:false });

or

$(window).on('beforeunload', function(){ // ajax here with async:false });

It's working fine. But in Chrome, it logs the following message:

Synchronous XMLHttpRequest on the main thread is deprecated because of its detrimental effects to the end user's experience. For more help, check http://xhr.spec.whatwg.org/.

I have googled again for the same and came to know that it is discouraging to use Ajax on unload event, and found following details from here

in short, they are against the use of ajax with async:false with window.unload or window.beforeUnload method. If I remove async param from Ajax, then it's not working as intended.

What is the right approach if I want to do some activity on server side if user closes browser window?

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Answer 1

I remember to be in a similar situation once where I needed to perform an action on server side once user closed the window. However, my research came to same conclusion as yours that is discouraged to use any type of ajax call on window unload events. So, my final approach was to set a specific Cookie on client side in the window unload event, and when the same user visited that page, only then I performed my required action and deleted the cookie from server side.

I know this is not exactly performing the action at the same time but that was the best approach which worked for me.