Blog
Mert Özen's blog posts on software development, backend, frontend, and DevOps.
Introduction to Generics in TypeScript: Taking the Type as a Parameter
Why generic functions exist, how a type parameter ties input to output, how TypeScript infers T, and how generics differ from any and unknown, with small examples.
Generic Constraints in TypeScript: extends, Default Types, const and NoInfer
We constrain type parameters with extends, tie two parameters together with keyof, use default type parameters, and steer inference with TS 5.0 const type parameters and TS 5.4 NoInfer.
Generic Interfaces, Types and Classes in TypeScript: Box, Result and Stack
We move type parameters from functions to types: Box<T> as a generic type alias, a paginated list as a generic interface, Result<T, E> for success and failure, and generic Stack and Registry classes.
Classes in TypeScript: Access Modifiers, abstract, implements and override
What TypeScript adds to classes: property types and initialization, public/private/protected versus #private, readonly, abstract, implements, override, and a note on parameter properties.
keyof and typeof in TypeScript: Deriving Types from Values and Keys
We derive types from values with type-level typeof, build unions from a type's keys with keyof, look at the index signature surprise, and use the keyof typeof pattern in practice.
TypeScript Indexed Access Types: Deriving Types from Existing Ones with T["key"]
We look at reading a property's type with T["key"], union indexes, getting an array's element type with T[number], T[K] in generics and deriving pieces from large API types.
TypeScript Utility Types 1: Partial, Required, Readonly, Pick, Omit and Record
We use Partial, Required, Readonly, Pick, Omit and Record with realistic examples, combine them in a form model and look at silent pitfalls such as a typo inside Omit.
TypeScript Utility Types 2: Exclude, Extract, NonNullable, ReturnType and More
We filter unions with Exclude, Extract and NonNullable, and derive types from functions and classes with ReturnType, Parameters, Awaited, InstanceType and ConstructorParameters.
TypeScript Type Guards: Type Predicates and Assertion Functions
We write type predicates with x is T and assertion functions with asserts, and look at TypeScript 5.5's inferred type predicates and narrowing arrays with filter, pitfalls included.
Asynchronous Code in TypeScript: Typing Promise, async and fetch Responses
We look at Promise<T> and async return types, why a fetch response is any, runtime validation with unknown and hand-written type guards, and the types of Promise.all and allSettled.
Modules in TypeScript: import type, verbatimModuleSyntax and File Extensions
We look at modules versus scripts in TypeScript, import type and export type, why verbatimModuleSyntax matters, .ts extensions in imports, and bundler versus nodenext resolution.
Error Handling in TypeScript: unknown in catch, Narrowing Errors and the Result Pattern
We look at why the catch variable is unknown, narrowing with instanceof Error, custom error classes, Promise pitfalls, and modeling errors with Result and discriminated unions.