How do big companies develop and deploy their web apps?

Hi, I'm a Web developer and I spend quite a lot time on GitHub. As I began to work last year, it becomes complex to me that, developing and deploying single page webapps is such a tough task. Because we have so many things to consider, and we cannot just package our apps just like a Chrome packaged apps. Here are some common things we need to consider: * debugging CSS with Workspace or Less, how to choose among them? * how to package CSS online, how many files, how to compile? * debugging HTML with Nginx, with a Web server, or something else? * to use CoffeeScript or some altjs languages? * combine code togather in debugging, with RequireJS or else? * packaging JS code on server is still different with that in development.. * how to deal with Retina pictures, CSS Sprites, even both? * multi-language support, with means we need to render on server or by lazy loading? * add MD5 to filenames, put them on CDN, wait, we need to modify HTML/CSS in order to load them? * and more.. Web is rolling fast with a bunch of new techniques and problems. I think it's really complex to build nice web apps. Do we have nice solution for dealing with these problems people may run into in build web apps?