The JavaScript programming language, developed by Netscape, Inc., is not part of the Java platform. JavaScript, does not create applets or stand-alone applications.

Java SE 6 makes it simple to use JavaScript within Java code. Other scripting engines can also be associated with Java, but it is handy to have one provided out-of-the-box with Mozilla Rhino.

JavaScript and Java scored high as both most liked and most disliked programming languages in JetBrains’ State of the Developer Ecosystem survey. Perl was far and away the most disliked language.

It's a bit unclear what you mean when you say "what can I do". If you're referring to specific language features that are available to Java or C++ that are not available to JavaScript, it would be ...

Python also ranked highly in Stack Overflow's 2017 developer survey, which found it was the fifth most popular language behind JavaScript, SQL, Java, and C#.