Joey Hess (joeyh) has been writing about this for a long time (because he uses dial-up at his home). Here is a recent thread about a 2016 blog post on this: https://news.ycombinator.com/item?id=13397282
> Please, please, if your site requires AJAX to work at all, then retry failed AJAX queries. Anyone here have information on the most reliable heuristics to do retries? Or information on the implementations used by say Gmail or Facebook?
Also, as a side note, any page that becomes unusable because an ajax request failed to return has some really broken design. Ajax retries are not a solution for that, go fix the design instead.