TypeScript Best Practices - Programming

The strict flag turns on a group of checks including strictNullChecks and noImplicitAny that catch many real bugs. strictNullChecks forces you to handle null and undefined explicitly, preventing a huge source of runtime crashes. Starting new projects with strict enabled gives you the full benefit of the type system from day one.

any disables type checking for a value, so the compiler stops catching mistakes and autocomplete degrades. Overusing it turns TypeScript back into untyped JavaScript. When a type is uncertain, prefer unknown and narrow it, or write a precise type. Reserve any for rare, isolated cases and document why it was necessary.

No, TypeScript's inference is strong, so annotating obvious types adds noise. Let inference handle local variables and return types where they are clear. Do add explicit annotations on function parameters, public APIs, and places where you want to enforce a specific contract, since those improve clarity and catch mismatches at boundaries.

Design your types so illegal combinations cannot compile. Instead of loose booleans and optional fields that allow contradictory states, use discriminated unions where each variant carries exactly the fields it needs. This pushes error detection to compile time, so the type system, rather than runtime checks, prevents your code from entering an impossible state.

In both, enable strict mode in tsconfig and avoid the any type so the compiler catches errors. For Angular, type component inputs and outputs, use interfaces for models, and type observables from services. For Express, type request and response objects, define interfaces for request bodies, and validate input at the boundary. Share type definitions between layers to keep contracts consistent.

Prefer union string literal types or const objects over enums when you want simpler output and easy narrowing, reserving enums for cases that benefit from them. Use ESLint with the TypeScript plugin to enforce consistent rules. For AWS Lambda and CDK, type event and context objects, keep infrastructure code strongly typed, and define interfaces for stack props to catch configuration mistakes early.

Type props and state explicitly rather than reaching for any, and let TypeScript infer where it can. Prefer typed hooks, model component props as interfaces, and use discriminated unions for variant states. Type event handlers with the React event types, avoid casting DOM nodes, and enable strict mode so missing cases surface at compile time instead of in the browser.

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