JavaScript Fundamentals 101

JavaScript (/ˈdʒɑːvɑːˌskrɪpt/; JS), also known as ECMAScript (the untrademarked name used for the standard), is a dynamic programming language.[5] It is most commonly used as part of web browsers, whose implementations allow client-side scripts to interact with the user, control the browser, communicate asynchronously, and alter the document content that is displayed.[5] It is also used in server-side network programming with runtime environments such as Node.js, game development and the creation of desktop and mobile applications.

JavaScript is classified as a prototype-based scripting language with dynamic typing and first-class functions. This mix of features makes it a multi-paradigm language, supporting object-oriented,[6] imperative, and functional[1][7] programming styles. [From Wikipedia.]
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Sample Code

Here is some simple JS code, also from the main Wikipedia page.

var sum = function() {
var i, x = 0;
for (i = 0; i < arguments.length; ++i) { x += arguments[i]; } return x; } sum(1, 2, 3); // returns 6