This book is writter for beginners of JavaScript, who are potential beginners to programming at all. It is written to serve as a practical introduction and not an academic textbook, but we intend to explain things precisely to avoid the risks of you getting things wrong.
JavaScript is a very popular programming language, especially for beginners. Many people with less programming experience have ever seen JavaScript, for example in Web apps. Javascript has become popular with the spread of client-side Web programming; however it is now common with Node.JS in server-side apps and command line programs. It is also a common choice as an automation/scripting language.
JavaScript is a multi-paradigm language. It is for example based on the tradition of functional programming, inherited from LISP. JavaScript is well known as an example of prototype-based object oriented programming language.
It is good for beginning programming with, because you can learn various styles of programming with it. It is also good because it is very popular, so JavaScript skills are very useful. Something very good but not so popular can be painful to learn, or use afterwards.
JavaScript is not a subset of Java, or anything directly connected with it, in spite of what it is called. However JavaScript is intentionally designed to look like Java, so that it looks familiar to those with experience with Java or other C-influenced popular programming languages.
JavaScript is standardised as ECMAScript, a global standard, at ECMA International.