7 TypeScript Patterns I Use in Every Project These patterns caught bugs before they reached production. Every single time. 1. The Discriminated Union Pattern // ❌ BAD: Using optional fields to distinguish states interface User { id : string ; email : string ; name ?: string ; // Is this "loading" or "no name"? error ?: string ; // Is this "error" or "no error"? } // ✅ GOOD: Discriminated union — every state is explicit type UserState = | { status : ' idle ' } | { status : ' loading ' } | { status : ' success ' ; user : { id : string ; email : string ; name : string } } | { status : ' error ' ; error : string }; function renderUser ( state : UserState ): string { // TypeScript KNOWS which fields exist in each state switch ( state . status ) { case ' idle ' : return ' Enter a user ID ' ; case ' loading ' : return ' Loading... ' ; case ' success ' : return `Hello, ${ state . user . name } ` ; // ✅ user is guaranteed here case ' error ' : return `Error: ${ state .…