javascript-typescript

Define a union of object types sharing a literal tag field, such as Result<T> with success: true or success: false variants. TypeScript narrows the type automatically when you check the tag, giving safe access to variant-specific properties.

Declare a generic function like useLocalStorage<T> that accepts a key and initial value, then use useState<T> and useEffect for persistence. Returning the state tuple as const preserves precise typing for consumers.

Enable strict, noUncheckedIndexedAccess, and noImplicitOverride in compilerOptions, with target ES2022 and moduleResolution bundler. These flags catch undefined index access and missing override modifiers at compile time.

Yes, optional chaining (?.) safely accesses nested properties while nullish coalescing (??) provides defaults only for null or undefined. Combined as user?.address?.city ?? 'Unknown', they avoid both runtime errors and falsey-value bugs.

Use Pick to derive a type with selected properties, such as a UserPreview, and Omit to exclude fields like id when creating new entities. They keep derived types synchronized with the source interface automatically.