What are the best practices for using type guards in TypeScript?

What are the best practices for using type guards in TypeScript?

Using type guards in TypeScript helps ensure type safety. Best practices include using user-defined type guards, leveraging the 'in' operator, and utilizing 'typeof' for primitive types.

Can you give me an example of a user-defined type guard?

Sure! A user-defined type guard can be a function that checks if an object is of a specific type. For example:

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

How do I use the 'in' operator for type guards?

You can use the 'in' operator to check if a property exists in an object. For example:

interface Dog { bark: () => void; }
interface Cat { meow: () => void; }

function isDog(pet: Dog | Cat): pet is Dog {
    return 'bark' in pet;
}

What are some common mistakes to avoid with type guards?

Common mistakes include not narrowing types correctly, using type assertions instead of type guards, and forgetting to handle all possible types in union types.