TypeScript Utility Types

TypeScript provides several global utility types to facilitate common type transformations.

Property Modifiers

• Partial<T>: Constructs a type with all properties of T set to optional.
• Required<T>: Constructs a type with all properties of T set to required (opposite of Partial).
• Readonly<T>: Constructs a type with all properties of T set to readonly.

Subset and Mapping

• Record<K, T>: Constructs an object type whose property keys are K and whose property values are T.
• Pick<T, K>: Constructs a type by picking the set of properties K (string literal or union of string literals) from T.
• Omit<T, K>: Constructs a type by picking all properties from T and then removing K.

Union Manipulation

• Exclude<T, U>: Excludes from T those types that are assignable to U.
• Extract<T, U>: Extracts from T those types that are assignable to U.
• NonNullable<T>: Excludes null and undefined from T.

Function and Class Types

• Parameters<T>: Obtains the parameters of a function type in a tuple.
• ReturnType<T>: Obtains the return type of a function type.
• ConstructorParameters<T>: Obtains the parameters of a constructor function type in a tuple.
• InstanceType<T>: Obtains the instance type of a constructor function type.

Advanced

• Awaited<T>: Models operations like await in async functions, or the .then() method on Promises.

References

• Source: 00_Raw/typescript-handbook.md
• typescript-moc
• typescript-generics
• typescript-conditional-types

• agent-note-conventions (Modeling metadata constraints)
• typescript-objects