023 - TS Utility Types

Usage

• Awaited<Type> unwrap promise type
• Partial<Type> set all properties optional
• Required<Type> set all required
• Readonly<Type> set all readonly
• Record<Keys, Type> a map type
• Pick<Type, Keys> pick keys to construct a type
• Omit<Type, Keys> pick all to remove keys to construct a type
• NonNullable<Type> exclude null and undefined
• Extract<Type, Union> extract all union members that are assignable to Union to construct a type
• Exclude<UnionType, ExcludedMembers> remove excluded members
• Parameters<Type> construct a tuple type from function parameters
• ConstructorParameters<Type>
• ReturnType<Type> function return type
• InstanceType<Type>
• ThisParameterType<Type> function this parameter type, else unknown
• OmitThisParameter<Type>
• ThisType<Type>
• Uppercase<StringType>
• Lowercase<StringType>
• Capitalize<StringType>
• Uncapitalize<StringType>

Partial Required Readonly

type MyPartial<T> = {
  [Key in keyof T]?: T[Key] | undefined
}
 
type MyRequired<T> = {
  [Key in keyof T]-?: T[Key]
}
 
type MyReadonly<T> = {
  readonly [Key in keyof T]: T[Key]
}

Record

type MyPropertyKey = string | number | symbol
 
type MyRecord<K extends PropertyKey, T> = {
  [Key in K]: T
}

Pick Omit

type MyPick<T, K extends keyof T> = {
  [Key in K]: T[Key]
}
 
type MyOmit<T, K extends keyof T> = {
  [Key in Exclude<keyof T, K>]: T[Key]
}

NonNullable

type MyNonNullable<T> = T & {}

Exclude Extract

type MyExclude<T, U> = T extends U ? never : T
 
type MyExtract<T, U> = T extends U ? T : never

Parameters ReturnType

type MyParameters<T extends (...args: any[]) => any> = T extends (...args: infer P) => any
  ? P
  : never
 
type MyReturnType<T extends (...args: any) => any> = T extends (...args: any) => infer R ? R : never

Thanks

• 024 - Create Types from Types
• TypeScript: Documentation
• Type Challenges