Learn TypeScript
Advantages of Type Predicates
Reusability
We can replicate some of the type checking by directly embedding inline checks into our functions such as:
(event.type === "click" or event.type === "keyboard") embedded directly within a handleEvent function.
But, if you need to check these types in other parts of your code, you’ll have to repeat these checks, which can lead to code duplication.
Having dedicated type guard functions like isClickEvent and isKeyboardEvent that use type predicates promotes reusability. These functions can be reused wherever you need to determine the type of an event, making the code more DRY (Don't Repeat Yourself).
Readability
The use of separate type guards can make the code more readable, especially in larger codebases.
It makes it clear that each check is a distinct operation with a specific purpose, improving maintainability.
Testing
It's harder to test the type checks in isolation if they are embedded inside functions.
With separate functions, you can easily write unit tests specifically for isClickEvent and isKeyboardEvent, ensuring each type guard behaves as expected independently of the handleEvent function.
Extensibility
If you need to extend the functionality by adding more event types, you’ll have to modify the handleEvent function, which could become unwieldy if it handles many event types.
The separate type guards allow you to extend functionality in a modular way. You can add new type guards and extend the handleEvent function more cleanly.
Summary
The separate type guard functions provide better reusability, readability, testability, and extensibility, making them preferable in larger or more complex codebases.