TypeScript ConstructorParameters<Type> Utility Type

The TypeScript ConstructorParameters<Type> utility type extracts the parameter types from a constructor function Type. It enhances type safety by enabling the creation of instances with correct constructor arguments, ensuring functions use the precise types expected by the constructor.

Syntax

type ConstructorParametersType = ConstructorParameters<Type>;

Parameters:

• ConstructorParametersType: The name of the type that represents the parameter types of the constructor function.
• Type: The constructor function type from which you want to extract the parameter types.

Example 1: Extracting Constructor Parameters for GFG Class

In this example, we define a class GFG with a constructor that accepts two string parameters. Using ConstructorParameters<typeof GFG>, we extract these parameter types. We then create a createGFG function that utilizes these types to instantiate GFG objects with varying parameter values.

// Define a class and its constructor
class GFG {
    constructor(name: string, course: string) {
        this.name = name;
        this.course = course;
    }
    name: string;
    course: string;
}

// Extract parameter types of the constructor
type GFGConstructorParams = ConstructorParameters<typeof GFG>;

// Create a function that creates an instance of the class
function createGFG(...params: GFGConstructorParams): GFG {
    return new GFG(...params);
}

const GFG1 = createGFG("GeeksforGeeks", "Java");
const GFG2 = createGFG("gfg", "Python");

console.log(GFG1);
console.log(GFG2); 

Output:

GFG { name: 'GeeksforGeeks', course: 'Java' }
GFG { name: 'gfg', course: 'Python' }

Example 2: Extracting Constructor Parameters for Rectangle Class

In this example, we create a Rectangle class with a constructor accepting two numbers: width and height. By using ConstructorParameters<typeof Rectangle>, we obtain the parameter types [number, number]. We then craft a createRectangle function using these types to generate Rectangle instances with distinct dimensions.

// Define a class and its constructor
class Rectangle {
    constructor(public width: number, public height: number) { }
}

// Extract parameter types of the constructor
type RectangleConstructorParams =
    ConstructorParameters<typeof Rectangle>;

// Create a function that creates an instance of the class
function createRectangle(...params: RectangleConstructorParams):
    Rectangle {
    return new Rectangle(...params);
}


const rect1 = createRectangle(5, 10);
const rect2 = createRectangle(8, 6);

console.log(rect1);
console.log(rect2); 

Output:

Rectangle { width: 5, height: 10 }
Rectangle { width: 8, height: 6 }