Did Facebook, Pinterest, Pandora, and other tech companies rewrote their whole product in Objective C?
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I've always wondered if Facebook rewrote their web app into Objective C so they could have an app on the iPhone...

I know Facebook and other major tech companies have their own iOS team but was there a converter or they rewrote the whole thing from scratch?
I can't imagine the CSS and server side scripting involved if they did. 
Anyways, please advise. 

Much thanks in advanced.