How do ES6 classes work?

Classes in ES6 and higher standards are a powerful tool for code structuring, but under the hood, they are arranged quite simply. Their core essence is that the class syntax is convenient syntactic sugar over JavaScript's familiar prototypal inheritance, sparing developers from the need to manually write constructor functions and configure prototype chains. A basic class definition looks like this: we use the class keyword followed by a name, and inside the body, we describe a special constructor() {} method, which is automatically called when creating a new instance via the new operator and serves to initialize the initial state of the object.

To implement a hierarchy and expand the capabilities of existing entities, an inheritance mechanism is used via the extends keyword, which allows the child class to adopt the functionality of the parent. At the same time, the child class constructor is required to call the super() function, which passes control to the parent constructor and initializes the this context. In practice, this looks like this: an Animal class is created with basic properties like a name, and then a Dog extends Animal class, which adds dog-specific methods.

An important feature of class implementation in JavaScript is that all methods declared inside the class body are automatically written to the constructor function's prototype, i.e., prototype. This provides significant RAM savings since instances do not duplicate methods on themselves, but share them through a common prototype chain. Each created object stores only its own unique properties, while borrowing methods from the common parent template.

Thus, classes combine a strict and understandable syntax familiar to programmers from other languages while preserving all the flexibility and lightweight nature of JavaScript's prototypal model. Using classes makes the codebase more readable and maintainable, especially in large team projects where component writing standardization plays a key role.