Which programming language is used to allow communication in web? Like on Facebook chat.
In Facebook they should use, among many other technologies, the programming language Hack (much similar to PHP) but more in general any back-end language can do the job. Oh, btw we do have a PHP course, check it out! https://www.sololearn.com/learning/1059/1801/3500/1
Communication on the web is generally enabled by the HTTP protocol. This is not tied to any specific programming language. You can write web applications in any language. https://en.m.wikipedia.org/wiki/Hypertext_Transfer_Protocol Facebook may be an interesting case study, but what they do on large scale, serving millions of requests every second, is completely different than a basic level project. So the fact that they are using PHP, Java, C++, Erlang, Haskell and even Python in their backend system, is not a practical pattern to follow for an average developer.