{"id":774,"date":"2025-08-18T21:27:38","date_gmt":"2025-08-19T03:27:38","guid":{"rendered":"https:\/\/kop.lat\/blog\/?p=774"},"modified":"2025-08-18T21:27:39","modified_gmt":"2025-08-19T03:27:39","slug":"built-in-utility-types-in-typescript","status":"publish","type":"post","link":"https:\/\/kop.lat\/blog\/built-in-utility-types-in-typescript\/","title":{"rendered":"Built-in utility types in Typescript"},"content":{"rendered":"\n

Comprehensive list of built-in utility types<\/strong> in TypeScript with a brief descriptio and examples for each:<\/p>\n\n\n\n

\n\n\n\n

TypeScript’s Built-in Utility Types<\/strong><\/h3>\n\n\n\n

1. Partial<Type><\/code><\/strong><\/h4>\n\n\n\n

Makes all properties of Type<\/code> optional.<\/p>\n\n\n\n

interface User { name: string; age: number; }\ntype PartialUser = Partial<User>; \/\/ { name?: string; age?: number }<\/code><\/pre>\n\n\n\n
2. Required<Type><\/code><\/strong><\/h4>\n\n\n\n
Makes all properties of Type<\/code> required (opposite of Partial<\/code>).<\/p>\n\n\n\n
type RequiredUser = Required<PartialUser>; \/\/ { name: string; age: number }<\/code><\/pre>\n\n\n\n
3. Readonly<Type><\/code><\/strong><\/h4>\n\n\n\n
Makes all properties of Type<\/code> read-only.<\/p>\n\n\n\n
type ReadonlyUser = Readonly<User>; \/\/ { readonly name: string; readonly age: number }<\/code><\/pre>\n\n\n\n
4. Record<Keys, Type><\/code><\/strong><\/h4>\n\n\n\n
Creates an object type with keys from Keys<\/code> and values of Type<\/code>.<\/p>\n\n\n\n
type UserMap = Record<string, User>; \/\/ { [key: string]: User }<\/code><\/pre>\n\n\n\n
5. Pick<Type, Keys><\/code><\/strong><\/h4>\n\n\n\n
Selects a subset of properties from Type<\/code> using Keys<\/code>.<\/p>\n\n\n\n
type UserName = Pick<User, 'name'>; \/\/ { name: string }<\/code><\/pre>\n\n\n\n
6. Omit<Type, Keys><\/code><\/strong><\/h4>\n\n\n\n
Removes properties Keys<\/code> from Type<\/code>.<\/p>\n\n\n\n
type AgelessUser = Omit<User, 'age'>; \/\/ { name: string }<\/code><\/pre>\n\n\n\n
7. Exclude<UnionType, ExcludedMembers><\/code><\/strong><\/h4>\n\n\n\n
Removes types from a union.<\/p>\n\n\n\n
type T = Exclude<'a' | 'b' | 'c', 'a'>; \/\/ 'b' | 'c'<\/code><\/pre>\n\n\n\n
8. Extract<UnionType, ExtractableMembers><\/code><\/strong><\/h4>\n\n\n\n
Keeps only the assignable types in a union.<\/p>\n\n\n\n
type T = Extract<'a' | 'b' | 1, string>; \/\/ 'a' | 'b'<\/code><\/pre>\n\n\n\n
9. NonNullable<Type><\/code><\/strong><\/h4>\n\n\n\n
Removes null<\/code> and undefined<\/code> from Type<\/code>.<\/p>\n\n\n\n
type T = NonNullable<string | null | undefined>; \/\/ string<\/code><\/pre>\n\n\n\n
10. Parameters<FunctionType><\/code><\/strong><\/h4>\n\n\n\n
Extracts parameter types of a function as a tuple.<\/p>\n\n\n\n
type FnParams = Parameters<(x: number, y: string) => void>; \/\/ [x: number, y: string]<\/code><\/pre>\n\n\n\n
11. ReturnType<FunctionType><\/code><\/strong><\/h4>\n\n\n\n
Extracts the return type of a function.<\/p>\n\n\n\n
type FnReturn = ReturnType<() => number>; \/\/ number<\/code><\/pre>\n\n\n\n
12. ConstructorParameters<ClassType><\/code><\/strong><\/h4>\n\n\n\n
Extracts constructor parameter types as a tuple.<\/p>\n\n\n\n
class Cat { constructor(name: string, age: number) {} }\ntype CatParams = ConstructorParameters<typeof Cat>; \/\/ [name: string, age: number]<\/code><\/pre>\n\n\n\n
13. InstanceType<ClassType><\/code><\/strong><\/h4>\n\n\n\n
Extracts the instance type of a class constructor.<\/p>\n\n\n\n
type CatInstance = InstanceType<typeof Cat>; \/\/ Cat<\/code><\/pre>\n\n\n\n
14. ThisParameterType<FunctionType><\/code><\/strong><\/h4>\n\n\n\n
Extracts the this<\/code> parameter type of a function.<\/p>\n\n\n\n
function fn(this: { x: number }) {}\ntype ThisType = ThisParameterType<typeof fn>; \/\/ { x: number }<\/code><\/pre>\n\n\n\n
15. OmitThisParameter<FunctionType><\/code><\/strong><\/h4>\n\n\n\n
Removes the this<\/code> parameter from a function type.<\/p>\n\n\n\n
type NoThisFn = OmitThisParameter<typeof fn>; \/\/ () => void<\/code><\/pre>\n\n\n\n
16. Awaited<Type><\/code><\/strong><\/h4>\n\n\n\n
Unwraps Promise<\/code> return types (useful for async functions).<\/p>\n\n\n\n
type T = Awaited<Promise<string>>; \/\/ string<\/code><\/pre>\n\n\n\n
17. Uppercase<StringType><\/code><\/strong><\/h4>\n\n\n\n
Transforms string literal types to uppercase.<\/p>\n\n\n\n
type Greeting = Uppercase<'hello'>; \/\/ \"HELLO\"<\/code><\/pre>\n\n\n\n
18. Lowercase<StringType><\/code><\/strong><\/h4>\n\n\n\n
Transforms string literal types to lowercase.<\/p>\n\n\n\n
type QuietGreeting = Lowercase<'HELLO'>; \/\/ \"hello\"<\/code><\/pre>\n\n\n\n
19. Capitalize<StringType><\/code><\/strong><\/h4>\n\n\n\n
Capitalizes the first letter of a string literal.<\/p>\n\n\n\n
type Name = Capitalize<'alice'>; \/\/ \"Alice\"<\/code><\/pre>\n\n\n\n
20. Uncapitalize<StringType><\/code><\/strong><\/h4>\n\n\n\n
Uncapitalizes the first letter of a string literal.<\/p>\n\n\n\n
type InformalName = Uncapitalize<'Alice'>; \/\/ \"alice\"<\/code><\/pre>\n\n\n\n
\n\n\n\n
Key Takeaways<\/strong><\/h3>\n\n\n\n
    \n
  1. Transformation Utilities<\/strong>:<\/li>\n<\/ol>\n\n\n\n
      \n
    • Modify existing types (Partial<\/code>, Readonly<\/code>, Pick<\/code>, Omit<\/code>).<\/li>\n<\/ul>\n\n\n\n
        \n
      1. Type Extraction<\/strong>:<\/li>\n<\/ol>\n\n\n\n
          \n
        • Get function\/constructor parameters (Parameters<\/code>, ConstructorParameters<\/code>).<\/li>\n\n\n\n
        • Extract return types (ReturnType<\/code>, Awaited<\/code>).<\/li>\n<\/ul>\n\n\n\n
            \n
          1. String Manipulation<\/strong>:<\/li>\n<\/ol>\n\n\n\n
              \n
            • Change string literal casing (Uppercase<\/code>, Capitalize<\/code>, etc.).<\/li>\n<\/ul>\n\n\n\n
                \n
              1. Advanced Use Cases<\/strong>:<\/li>\n<\/ol>\n\n\n\n
                  \n
                • Record<\/code> for dictionary types, NonNullable<\/code> for strict null checks.<\/li>\n<\/ul>\n\n\n\n
                  \n\n\n\n
                  Example: Combining Utilities<\/strong><\/h3>\n\n\n\n
                  \/\/ Create a read-only subset of an API response\ntype ApiResponse = {\n  id: number;\n  name: string;\n  email?: string;\n};\n\ntype SafeResponse = Readonly<Pick<ApiResponse, 'id' | 'name'>>;\n\/\/ { readonly id: number; readonly name: string }<\/code><\/pre>\n\n\n\n
                  These utilities help write type-safe, maintainable code<\/strong> with minimal boilerplate. <\/p>\n","protected":false},"excerpt":{"rendered":"
                  Comprehensive list of built-in utility types in TypeScript with a brief descriptio and examples for each: TypeScript’s Built-in Utility Types 1. Partial<Type> Makes all properties of Type optional. 2. Required<Type> Makes all properties of Type required (opposite of Partial). 3. Readonly<Type> Makes all properties of Type read-only. 4. Record<Keys, Type> Creates an object type with […]<\/p>\n","protected":false},"author":1,"featured_media":232,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[49],"tags":[23,63],"_links":{"self":[{"href":"https:\/\/kop.lat\/blog\/wp-json\/wp\/v2\/posts\/774"}],"collection":[{"href":"https:\/\/kop.lat\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/kop.lat\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/kop.lat\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/kop.lat\/blog\/wp-json\/wp\/v2\/comments?post=774"}],"version-history":[{"count":1,"href":"https:\/\/kop.lat\/blog\/wp-json\/wp\/v2\/posts\/774\/revisions"}],"predecessor-version":[{"id":775,"href":"https:\/\/kop.lat\/blog\/wp-json\/wp\/v2\/posts\/774\/revisions\/775"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/kop.lat\/blog\/wp-json\/wp\/v2\/media\/232"}],"wp:attachment":[{"href":"https:\/\/kop.lat\/blog\/wp-json\/wp\/v2\/media?parent=774"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/kop.lat\/blog\/wp-json\/wp\/v2\/categories?post=774"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/kop.lat\/blog\/wp-json\/wp\/v2\/tags?post=774"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}