TypeScript5

TypeScript Best Practices

tsconfig.json Configuration

• Enable strict mode (or individual strict flags like strictNullChecks, noImplicitAny, strictFunctionTypes, etc.). This is the most crucial step for leveraging TypeScript's safety features.
• Configure target and module appropriately for your runtime environment (e.g., ES2022 or higher for modern Node/browsers, appropriate module system like NodeNext or ESNext).
• Set up baseUrl and paths for non-relative module resolution if needed, especially in larger projects or monorepos.
• Understand compiler options related to JSX (jsx, jsxFactory, etc.) if using React/JSX.
• Configure declaration file generation (declaration, declarationMap, outDir) if building a library.

Type System & Definitions

• Avoid any. Use unknown when the type is truly unknown and perform type checking/narrowing before use.
• Use explicit types for function parameters, return values, and variable declarations where inference is not sufficient or clear.
• Prefer specific types over overly broad ones (e.g., string over any, "success" | "error" over string).
• Use interface for defining the shape of objects or implementing classes.
• Use type for creating aliases for unions, intersections, tuples, primitives, and using utility types.
• Leverage built-in Utility Types (Partial, Required, Readonly, Pick, Omit, Record, etc.) to manipulate existing types effectively.
• Use Generics (<T>) to create reusable components, functions, and types that can work over a variety of types.
• Use readonly modifiers for properties that should not be reassigned after object creation.
• Utilize Discriminated Unions (tagged unions) with literal types to create type-safe state machines or variant types.

Type Narrowing & Guards

• Rely on TypeScript's control flow analysis for automatic type narrowing (e.g., within if checks, switch statements, instanceof checks).
• Use typeof checks for primitives.
• Use instanceof checks for classes.
• Use the in operator to check for property existence.
• Create custom Type Guard functions (value is Type) for complex validation logic.