What are some examples of type guards in TypeScript?

What are some examples of type guards in TypeScript?

Type guards in TypeScript are techniques used to narrow down the type of a variable. For example, you can use the typeof operator to check if a variable is a string.

Can you show me a code example of using typeof as a type guard?

Sure! Here's a simple example:

function printLength(value: string | number) {
    if (typeof value === 'string') {
        console.log(value.length);
    } else {
        console.log('Not a string');
    }
}

This function checks if value is a string and prints its length.

What about using instanceof as a type guard?

Great question! The instanceof operator can be used to check if an object is an instance of a specific class. Here's an example:

class Dog {
    bark() {
        console.log('Woof!');
    }
}

function makeSound(animal: Dog | string) {
    if (animal instanceof Dog) {
        animal.bark();
    } else {
        console.log('Not a Dog');
    }
}