Basics

// Define a class with properties and methods
class MyClass {
  // define properties
  private privateField: string;
  public publicField: number;

  // Constructor to initialize the class
  constructor(privateField: string, publicField: number) {
    this.privateField = privateField;
    this.publicField = publicField;
  }

  // define methods
  // Method with parameters and return type
  public calculateSum(x: number, y: number): number {
    return x + y;
  }

  // Getter method
  getPrivateField(): string {
    return this.privateField;
  }
}

// Create an instance of the class
const myInstance = new MyClass("PrivateValue", 42);

// Access fields and methods
console.log(myInstance.publicField); // Output: 42
console.log(myInstance.calculateSum(5, 3)); // Output: 8
console.log(myInstance.getPrivateField()); // Output: PrivateValue

Properties

In TS, each member is public by default

Private Properties

Private properties get create by using a # prefix and cannot be legally referenced outside of the class

private Keyword

private keyword is a compile time annotation

• Compiler understands that the property should only be accessible inside that class
• private keyword is not enforced at runtime
• JS code emitted after compiling is a regular field and not a # private field in JS

Private Methods

Private methods cannot be defined directly in an interface as interfaces are meant to declare the public contract of a class

Getters, Setters, and Generators

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

  // Define Getter
  get area() {
    return this.calcArea();
  }

  // Define method
  calcArea() {
    return this.height * this.width;
  }

  // generators "yield" results
  // has its own state to track the call count to "yield" different results
  *getSides() {
    yield this.height;
    yield this.width;
    yield this.height;
    yield this.width;
  }
}

const square = new Rectangle(10, 10);

console.log(square.area); // 100
console.log([...square.getSides()]); // [10, 10, 10, 10]