It allows you to add interactivity to your Web sites;
It is powerful, easy to learn, and quick to write;
It has great tools (editors, runtimes, lint tools, browsers, and third party libraries) as well as great online support through plenty of active open source communities.
Your first HTML/CSS/JS page
Variables, values, functions, operators, and expressions
Module 2: Adding interactivity to HTML
Conditional statements, loops and logical operators