TypeScript Patterns Every Developer Should Know in 2026

TypeScript has matured far beyond "JavaScript with types." The type system is powerful enough to encode complex business logic at compile time. Here are the patterns that make the biggest difference in production codebases. Discriminated Unions Model states where different variants carry different data. TypeScript narrows the type automatically based on the discriminant. type AsyncState < T > = | { status : " idle " } | { status : " loading " } | { status : " success " ; data : T } | { status : " error " ; error : Error } function renderState < T > ( state : AsyncState < T > ) { switch ( state . status ) { case " idle " : return " Ready " case " loading " : return " Loading... " case " success " : return `Data: ${ JSON . stringify ( state . data )} ` case " error " : return `Error: ${ state . error . message } ` } } This is the foundation of type-safe state management. Every React app with async data should use this pattern instead of separate isLoading , isError , data booleans. Brand