You’re building a simple form and need to handle user profile data: name, email, and age. You want strong TypeScript type checking, clean code, and something easy to refactor later. But now you’re stuck: should this be a class or an interface? This question shows up everywhere, API response models, form validation, domain models, even small utility objects. Sometimes you … Read more >>
Imagine you just finished wiring up a fetchUserProfile API in your React app. The backend sends you a JSON response with fields like name, email, isEmailVerified, and a nested address object. You log the data, it looks fine, but your editor keeps yelling because everything is typed as any and you lose auto-complete the moment … Read more >>
You build a form, define a nice TypeScript type for your form data, submit it… and suddenly half your fields are undefined. You try to patch values inside the function, but your code starts to feel messy and you lose confidence in your type safety. A cleaner way is to design your types and helper … Read more >>
When TypeScript shows the error “Property does not exist on type…”, it usually appears in the middle of a refactor or when you are consuming an API, and can be confusing because the property clearly exists at runtime. This error is TypeScript’s way of telling you that the type you are working with does not … Read more >>
When you “check the type” of a variable in TypeScript, you’re really checking the runtime value and letting the compiler narrow the static type for you. In this tutorial, I’ll walk through the practical ways to do that using typeof, instanceof, and type guards, with examples you can drop into real projects. How to check the type … Read more >>
If you’ve ever tried to write this in TypeScript: interface User { firstName: string; lastName: string; age: number = 30; // ❌} …you’ve seen the error and thought, “Wait, how do I give this a default?” Interfaces only describe shape; they don’t exist at runtime, so they can’t hold default values. But in real projects, … Read more >>
In TypeScript, “TypeError: is not a function” is a runtime JavaScript error that appears when you try to call something with () that is not actually a function. The value might be a string, an object, undefined, null, or some other type that cannot be called. Most of the time, this happens because the variable you are calling does … Read more >>
TypeScript interfaces can absolutely have functions, and there are several useful patterns beyond the basic “add a method and implement it in a class.” In this tutorial, I’ll walk you through those patterns in a practical, no-nonsense way. Why put functions in a TypeScript interface? When I say “functions in an interface,” I’m really talking … Read more >>
If you’ve ever copied and pasted the same function logic three times just to handle string, number, and boolean separately, TypeScript generic anonymous functions are the fix. They let you write one flexible, type-safe function expression that adapts to any data type, without losing IntelliSense or compile-time safety. In this tutorial, I’ll walk you through exactly how TypeScript generic … Read more >>
TypeScript is very good at guessing (inferring) the return type of your arrow functions, but in real projects, “good enough” inference can still hide bugs. In this tutorial, I’ll walk through how to explicitly specify the return type for arrow functions in TypeScript, and more importantly, when it actually matters. We’ll start with the basics, then move … Read more >>