How do I use type guards in TypeScript?

How do I use type guards in TypeScript?

Type guards in TypeScript are techniques used to narrow down the type of a variable. They help ensure type safety.

Can you give me an example of a type guard?

Sure! Here's a simple example:

function isString(value: any): value is string {
    return typeof value === 'string';
}

const input: any = 'Hello, TypeScript!';
if (isString(input)) {
    console.log(input.toUpperCase()); // Safe to call string methods
}

What are the different types of type guards?

There are several types of type guards:

1. typeof: Checks the type of a variable (e.g., string, number).
2. instanceof: Checks if an object is an instance of a class.
3. User-defined type guards: Functions that return a type predicate.

How do I create a user-defined type guard?

You can create a user-defined type guard by defining a function that returns a type predicate. For example:

function isCat(animal: Animal): animal is Cat {
    return (animal as Cat).meow !== undefined;
}