Difference in site functionality on some websites

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I was going different websites on opera mini in my phone and found that some websites like Amazon, Flipkart are displayed differently in the browser. Specially the javascript functionalities like Side menu animation or search functionality loads on the client side (or atleast it seems). And some websites do not support this. What can this be related to and if I want to to implement this on my website, how do i do it?

Please help.

Thanks!

I didn't find the right solution from the Internet.

References forums.opera.com/topic/22520/difference-in-site-functionality-on-some-websites-flipkart-amazon

Hand Drawn animation