50K Array sorted in:

As you can see, without Web Worker, your browser maybe able to sort the 50K Array but you can't work with your browser while sorting and also your browser won't render anything until sorting ends, that's why you can't see the animated progress bar in the page.

Your browser sorted 50K Array without any crash or lagging, because your browser supports Web Worker. When you do a job with Web Worker, it's just like when you run a program in another thread. Also you can see the animated progress bar while sorting.