JavaScript is the programming language of HTML and the Web. JavaScript and Java are completely different languages, both in concept and design.
JavaScript was invented by Brendan Eich in 1995, and became an ECMA standard in 1997.
ECMA-262 is the official name of the standard. ECMAScript is the official name of the language.

The <script> Tag

In HTML, JavaScript code must be inserted between <script> and </script> tags

Why Study JavaScript?

JavaScript is one of the 3 languages all web developers must learn:
   1. HTML to define the content of web pages
   2. CSS to specify the layout of web pages
   3. JavaScript to program the behavior of web pages
Web pages are not the only place where JavaScript is used. Many desktop and server programs use JavaScript. Node.js is the best known. Some databases, like MongoDB and CouchDB, also use JavaScript as their programming language.

JavaScript Can Change HTML Content

One of many JavaScript HTML methods is getElementById().

JavaScript Can Change HTML Attribute Values

JavaScript Can Change HTML Styles (CSS)

JavaScript Can Hide HTML Elements

JavaScript Can Show HTML Elements