Not simultaneous, but it does queue them with some parallelism (6 request for chrome IIRC). Page basically dies; any Ajax requests are at the back of the queue

Not simultaneous, but it does queue them with some parallelism (6 request for chrome IIRC). Page basically dies; any Ajax requests are at the back of the queue. Scroll halfway down that page, you'll be waiting 5 mins for the images in viewport to load since they are processed in order. You can roll your own lazy load, but it's a pain and often done poorly. A good browser implementation would be great for most pages (but 10k+ might still require custom work).