What is Public Static Const in TypeScript ?

In TypeScript, there is no direct equivalent to a public static const declaration as you might find in some other languages. However, you can achieve similar behavior using a combination of the public, static, and readonly keywords.

Syntax:

class ClassName {
  public static readonly CONSTANT_NAME: Type = InitialValue;
  // Other members of the class...
}

Let’s break down what each of these modifiers does:

• public: This keyword declares that the constant is accessible from outside the class. It means that the constant can be accessed by instances of the class as well as from outside the class.
• static: The static the keyword indicates that the constant is associated with the class itself, not with instances of the class. It means you can access the constant using the class name without creating an instance. For example, if you have a class MyClass with a static constantMY_CONSTANT, you can access it MyClass.MY_CONSTANT without creating an instance of MyClass.
• readonly: This keyword specifies that the constant cannot be reassigned after it is initialized. Once a value is assigned to a readonly property or constant, it cannot be changed. This ensures that the constant maintains its initial value throughout the program.

Example 1: In this example, the class MathConstants declares a public, static, and read-only constant named PI with the value 3.14159. The class also has a method calculateCircumference that uses the PI constant to calculate the circumference of a circle. The constant can be accessed using MathConstants.PI.

Javascript

class MathConstants {
    public static readonly PI: number = 3.14159;

    calculateCircumference(radius: number): number {
        return 2 * MathConstants.PI * radius;
    }
}

// Example usage:
const mathInstance = new MathConstants();
const circumference = mathInstance
    .calculateCircumference(5);
console.log(`Circumference: ${circumference}`);

Output:

Circumference: 31.4159

Example 2: In this simple example, the SimpleExample class declares a public, static, and read-only constant named GREETING with the value "Hello, TypeScript!". The class also has a method printGreeting that prints the greeting to the console. The constant is accessed using SimpleExample.GREETING.

Javascript

class SimpleExample {
    public static readonly GREETING:
        string = "Hello, TypeScript!";

    printGreeting(): void {
        console.log(SimpleExample.GREETING);
    }
}

// Example usage:
const instance = new SimpleExample();
instance.printGreeting();

Output:

Hello, TypeScript!