JavaScript Class

Classes are in fact “special functions”, and just as you can define function expressions and function declarations, the class syntax has two components: class expressions and class declarations.

Class declarations

class Rectangle {
  constructor(height, width) {
    this.height = height;
    this.width = width;
  }
}
 
const R1 = new Rectangle();

// unnamed
let Rectangle = class {
  constructor(height, width) {
    this.height = height;
    this.width = width;
  }
};
console.log(Rectangle.name);
// output: "Rectangle"
 
// named
let Rectangle = class Rectangle2 {
  constructor(height, width) {
    this.height = height;
    this.width = width;
  }
};
console.log(Rectangle.name);
// output: "Rectangle2"

Static Properties

Static properties are a group of class features that are defined on the class itself, rather than on individual instances of the class. These features include:

• Static methods
• Static fields
• Static getters and setters

Super

In JavaScript, super refers to the parent class constructor. (In our example, it points to the React.Component implementation.)
Importantly, you can’t use this in a constructor until after you’ve called the parent constructor. JavaScript won’t let you:

JavaScript Hoisting