Your problem is, that the subsequent calls to the ajaxrequest are using the same global variable for the request. The posted answer is right in the point to make the calls synchronous. Other thing...

What makes a difference between ajax and iframe approach is the use of dom model. Ajax takes this as one of it's base concepts.

This same goes for the original question - use dom to add/remove the...

There are more ways to do it than just cookies - it basicaly depends if you want to store the session between visits that happend at the same time, or if you want to save sessions for later use.
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This solution is not really a sleep. It effectively postpones the execution of function called by the setTimeout method, but javasctipy is asynchronous, so the execution of the commands following the...