JavaScript is the most popular scripting language on the internet, and works in all major browsers, such as Internet Explorer, Firefox, Chrome, Opera, and Safari.
What You Should Already Know

Before you continue you should have a basic understanding of the following:

   
What is JavaScript?

    JavaScript was designed to add interactivity to HTML pages
    JavaScript is a scripting language
    A scripting language is a lightweight programming language
    JavaScript is usually embedded directly into HTML pages
    JavaScript is an interpreted language (means that scripts execute without preliminary compilation)
    Everyone can use JavaScript without purchasing a license

Are Java and JavaScript the same?

NO!

Java and JavaScript are two completely different languages in both concept and design!

Java (developed by Sun Microsystems) is a powerful and much more complex programming language - in the same category as C and C++.
What Can JavaScript do?

    JavaScript gives HTML designers a programming tool - HTML authors are normally not programmers, but JavaScript is a scripting language with a very simple syntax! Almost anyone can put small "snippets" of code into their HTML pages
    JavaScript can react to events - A JavaScript can be set to execute when something happens, like when a page has finished loading or when a user clicks on an HTML element
    JavaScript can read and write HTML elements - A JavaScript can read and change the content of an HTML element
    JavaScript can be used to validate data - A JavaScript can be used to validate form data before it is submitted to a server. This saves the server from extra processing
    JavaScript can be used to detect the visitor's browser - A JavaScript can be used to detect the visitor's browser, and - depending on the browser - load another page specifically designed for that browser
    JavaScript can be used to create cookies - A JavaScript can be used to store and retrieve information on the visitor's computer

JavaScript = ECMAScript

JavaScript is an implementation of the ECMAScript language standard. ECMA-262 is the official JavaScript standard.

JavaScript was invented by Brendan Eich at Netscape (with Navigator 2.0), and has appeared in all browsers since 1996.

The official standardization was adopted by the ECMA organization (an industry standardization association) in 1997.

The ECMA standard (called ECMAScript-262) was approved as an international ISO (ISO/IEC 16262) standard in 1998.

The development is still in progress.