Typescript Tutorial #40 User-defined Type Guards

User-defined Type Guards:
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User Defined Type Guards mean that the user can declare a particular Type Guard or you can help TypeScript to infer a type when you use

we check whether a given animal is a Cat or a Dog

interface Cat {
meow(): void;
}

You have defined two interfaces, Cat and Dog, each representing a different type of animal. Cat has a method meow, and Dog has a method bark.

interface Cat {
meow(): void;
}

interface Dog {
bark(): void;
}

function isCat(animal: Cat | Dog): animal is Cat {
return 'meow' in animal;
}

You've created a user-defined type guard function called isCat. This function takes an animal parameter of type Cat | Dog, which means it can accept User Defined Type Guards mean that the user can declare a particular Type Guard or you can help TypeScript to infer a type when you use
values that are either a Cat or a Dog. The purpose of this function is to determine if the provided animal is a Cat or not. It does so by checking if the meow property exists in the animal object. If it does, the function returns true, indicating that it's a Cat. Otherwise, it returns false.

TypeScript uses the isCat type guard to narrow down the type of animal within each branch of the if statement, ensuring that you only call the appropriate methods based on the actual type of the animal. This helps prevent type-related errors at compile-time and improves the safety and correctness of your code when dealing with complex type hierarchies and union types.

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