Javscript and Java are two different computer languages, both developed in the same year. Java is object oriented that essentially means it can run on it’s own in a server environment. It is a very versatile and powerful language that is also a hard one to learn. If you know C++ or C# then your skills should be transferable to make the switch much easier. Java runs on many machines all over the workd, from enterprise systems, android apps, payment processing technologies and all manner of other software. It is also big in the IoT arena which has become a very popular and growing industry as of late (internet of things).
Conversely, Java script is a lightweight text based programming language that is designed to run within a web based application environment. It was originally meant to be a Java addon, but it soon took on a life of it’s own and become one of the three main pillars of any web development project; the other two being html and css.
JS can often be in multiple files included in the same webpage, and on other webpages within a site. On page SEO needs to factor in js load times, and sometimes lazy load (or delayed load) is required to give the best user experience.
PHP is a tried and tested server side language that enables data transfer from server to application and back again. Calling a phpinfo.php file like this can tell you what version of PHP is running on your webserver. Many CMS (content management systems) use php like wordpress or the less popular drupal or joomla.
PHP is the most common server side language used in web apps bit the burgeoning use of node.js is gaining a strong following as it is more streamlined than PHP.
I am a Digital Marketing and Organic SEO professional with over 20 years experience building and ranking websites. From small to large sites (including founding what is now one of the largest car forums in the world almost 15 years ago), I've been there and got the t-shirt and share my daily musings from working in search marketing full time!