Skip to main content

Advanced Types in TypeScript

In this section, you'll delve into advanced TypeScript types, which enable you to express more complex relationships between data structures and provide additional tools for type safety and flexibility in your code.

1. Intersection Types​

Intersection types allow you to combine multiple types into one, creating a type that possesses all the properties and methods of each constituent type.

Example -

typescript
interface Dog {
    bark(): void;
}

interface Cat {
    meow(): void;
}

type Pet = Dog & Cat;

class DogImpl implements Dog {
    bark(): void {
        console.log("Woof! Woof!");
    }
}

class CatImpl implements Cat {
    meow(): void {
        console.log("Meow! Meow!");
    }
}

function makePet(): Pet {
    return new DogImpl() as Pet;
}

let pet: Pet = makePet();
pet.bark(); // Output: Woof! Woof!
pet.meow(); // Output: Error: Property 'meow' does not exist on type 'Pet'.

2. Type Guards​

Type guards are runtime checks that allow TypeScript to infer more specific types within certain code paths, enhancing type safety and enabling more precise type checking.

Example -

typescript
function isNumber(x: any): x is number {
    return typeof x === "number";
}

function processValue(value: string | number): void {
    if (isNumber(value)) {
        console.log(value * 2);
    } else {
        console.log(value.toUpperCase());
    }
}

processValue(10); // Output: 20
processValue("hello"); // Output: HELLO

3. Type Casting​

Type casting allows you to assert the type of a value, informing TypeScript's type system of your intent and enabling you to perform operations that require a specific type.

Example -

typescript
let someValue: any = "hello";
let strLength: number = (someValue as string).length;
console.log(strLength); // Output: 5

4. Type Assertions​

Type assertions provide a way to override TypeScript's type inference and explicitly specify the type of a variable, giving you more control over type checking and enabling you to work with external data sources or dynamic values.

Example -

typescript
let someValue: any = "hello";
let strLength: number = (someValue as string).length;
console.log(strLength); // Output: 5