1. Easy to get started. Just a text editor and your favorite browser with a console to debug your code. Other languages require you to setup an environment and even install server software on your local machine but not JavaScript. You already have the tools to program in JavaScript on any computer you already use. Here is a demo of tools included with Google Chrome browser to debug and test JavaScript.
2. It's client side. Meaning things happen instantly on your local computers web browser or on any device. Edit something and see the results instantly. No need to upload files via ftp to your web host to see changes.
3. You are not constricted.Even if you use a library such as jQuery. you are not boxed in. Imagine if you had to program everything the way a JavaScript library wants. For example you can use a jQuery selector but you can do a for loop with plain JavaScript instead of using ".each" from jQuery library.
4. It's a scripting language When programming in JavaScript you are writing readable code that can easily be read by anyone if you use proper formatting, comments and naming conventions.
5. It's fun. Manipulating websites after they are loaded on users browser is fun. Known as dom scripting and it's done with JavaScript.
6. Used for interactivity Most interactive elements of websites are done using javascript.
7. Program with same on server side. Javascript can also work on the server side. With node js server software you can have parts of your application behind the scene on your server and interactive things available to users browser or client side.
8. It might be the future The most popular mobile development frameworks of today have developed a layer allowing JavaScript programmers to make mobile apps. Other devices and appliance makers might build API to allow you to build Apps and customize with JavaScript.
9. It's the foundation of any website. HTML markup, CSS stylesheet, and JavaScript programming.

So, how can you learn it?

If you enjoy project based learning. There is a book titled DOM Scripting Try a few examples in the book with a text editor and your favorite web browser. At first you will make mistakes, web browser console will let you know when you do and along the way you will become a developer.