Traditionally the server side of web applications has been written in PHP, Perl, Python, Java, C/C++, etc. Javascript traditionally was implemented only in web browsers, and hence Javascript programming has been almost completely focused on the client end of web application development. It's arguably better to have the same programming language on both client and server sides of web application development, maybe. Several attempts have been made to implement javascript for server side web application development. A new javascript stack, Node.JS, is getting a lot of attention.