JavaScript is a versatile programming language used to create dynamic and interactive content on websites. It runs in the browser and can manipulate HTML and CSS, making webpages responsive to user actions.

Although they share a similar name, Java and JavaScript are distinct languages. Java is a full-fledged programming language used primarily for server-side and application development, while JavaScript is mainly for web development and runs in the browser.

JavaScript has several data types, including: Primitive types: String, Number, Boolean, Null, Undefined, and Symbol (ES6). Object: This includes objects, arrays, and functions, which are considered non-primitive.

A variable is a container for storing data values. Variables in JavaScript are declared using var, let, or const.

var: Has function scope and is hoisted to the top of its scope, which can lead to unexpected behavior. let: Has block scope and is not hoisted in the same way as var. const: Also has block scope and is used for variables that should not be reassigned. The value itself is not immutable, but the reference is.