Low-level languages like C, have manual memory management primitives such as malloc() and free(). In contrast, JavaScript automatically allocates memory when objects are created and frees it when they are not used anymore (garbage collection). This automaticity is a potential source of confusion: it can give developers the false impression that they don't need to worry about memory management.

Boolean values can be one of two values: true or false, representing the truth value of a logical proposition.

Classes are a template for creating objects. They encapsulate data with code to work on that data. Classes in JS are built on prototypes but also have some syntax and semantics that are unique to classes.

Functions are one of the fundamental building blocks in JavaScript. A function in JavaScript is similar to a procedure—a set of statements that performs a task or calculates a value, but for a procedure to qualify as a function, it should take some input and return an output where there is some obvious relationship between the input and the output. To use a function, you must define it somewhere in the scope from which you wish to call it.

The encodeURIComponent() function encodes a URI by replacing each instance of certain characters by one, two, three, or four escape sequences representing the UTF-8 encoding of the character (will only be four escape sequences for characters composed of two surrogate characters). Compared to encodeURI(), this function encodes more characters, including those that are part of the URI syntax.

The typeof operator returns a string indicating the type of the operand's value.

The let declaration declares re-assignable, block-scoped local variables, optionally initializing each to a value.

The BigUint64Array typed array represents an array of 64-bit unsigned integers in the platform byte order. If control over byte order is needed, use DataView instead. The contents are initialized to 0n unless initialization data is explicitly provided. Once established, you can reference elements in the array using the object's methods, or using standard array index syntax (that is, using bracket notation).

JavaScript is a prototype-based language — an object's behaviors are specified by its own properties and its prototype's properties. However, with the addition of classes, the creation of hierarchies of objects and the inheritance of properties and their values are much more in line with other object-oriented languages such as Java. In this section, we will demonstrate how objects can be created from classes.

Whereas HTML defines a webpage's structure and content and CSS sets the formatting and appearance, JavaScript adds interactivity to a webpage and creates rich web applications.