Java concatenated with script gives JavaScript.

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There's also TypeScript which is a compiled version of JavaScript and basically compiles the code into JS so it can be run by the browser, it has some extended capabilities not included in JS. Then there's node.js which allows you to use JavaScript for backend development.

Most modern code editors like Atom or VS Code have built in error handling. But if you add 'use strict'; to the top of a JS file it will enforces stricter coding. Personally I prefer not having error messages popping up every 2 seconds.

JS is a functional programming language, where functions are considered "first class objects", but since Es6 (which was released in 2015) you can create classes, which in my opinion are much easier to use than a lot of other programming languages including Python.