JavaScript is a lightweight, interpreted programming language with object-oriented capabilities that allows you to build interactivity into otherwise static HTML pages. The general-purpose core of the language has been embedded in Netscape, Internet Explorer, and other web browsers.Javascript is very easy to implement because it is integrated with HTML.

Why to Learn Javascript

JavaScript is a programming language used primarily by Web browsers to create a dynamic and interactive experience for the user.Most of the functions and applications that make the Internet indispensable to modern life are coded in some form of JavaScript.

• JavaScript is a scripting or programming language that allows you to implement complex features on web pages — every time a web page does more than just sit there and display static information for you to look at — displaying timely content updates, interactive maps, animated 2D/3D graphics, scrolling video jukeboxes, etc. — you can bet that JavaScript is probably involved. It is the third layer of the layer cake of standard web technologies, two of which (HTML and CSS) we have covered in much more detail in other parts of the Learning Area.
• JavaScript is a lightweight interpreted programming language. The web browser receives the JavaScript code in its original text form and runs the script from that. From a technical standpoint, most modern JavaScript interpreters actually use a technique called just-in-time compiling to improve performance; the JavaScript source code gets compiled into a faster, binary format while the script is being used, so that it can be run as quickly as possible. However, JavaScript is still considered an interpreted language, since the compilation is handled at run time, rather than ahead of time.
• Scripts loaded using the defer attribute (see below) will run in the order they appear in the page and execute them as soon as the script and content are downloaded:
• As with HTML and CSS, it is possible to write comments into your JavaScript code that will be ignored by the browser, and exist to provide instructions to your fellow developers on how the code works (and you, if you come back to your code after six months and can't remember what you did). Comments are very useful, and you should use them often, particularly for larger applications. There are two types:
• So learning the language of Javascript is cool but mostly I recommend people start with a few things they are interested in building and then go from there. Unguided projects are where you will really start to understand what a browser is useful for (showing visual things to users) and what a server is useful for (passing messages between the browser and a database).
• The easiest way to understand how frameworks and libraries work together is to imagine you are building a house. The framework provides the foundation and the structure, while the library enables you to add in ready-made components (like furniture) rather than building your own from scratch.