Typescript Type calculation and manipulation (Utility Types)

typescript_type_calculation.ts

/**
 * TypeScript Type Calculations (Utility Types)
 */

/** ==================
 * Interface
==================== */

/** Example */
interface Person {
    name: String;
    age?: number;
    isMale ?: boolean;
}

/* ----- Partial ----- */

type PersonOptional = Partial<Person>

// type PersonOptional = {
//     name?: String | undefined;
//     age?: number | undefined;
//     isMale?: boolean | undefined;
// }


/* ----- Required ----- */

type PersonRequired = Required<Person>

// type PersonRequired = {
//     name: String;
//     age: number;
//     isMale: boolean;
// }

/* ----- Readonly ----- */

type PersonReadonly = Readonly<Person>

// type PersonReadonly = {
//     readonly name: String;
//     readonly age?: number | undefined;
//     readonly isMale?: boolean | undefined;
// }


/* ----- Pick ----- */

type PersonPick = Pick<Person, 'name' | 'age'>

// type PersonPick = {
//     name: String;
//     age?: number | undefined;
// }


/* ----- Omit ----- */

type PersonOmit = Omit<Person, 'age' | 'isMale' | 'x'>

// type PersonOmit = {
//     name: String;
// }


/** ==================
 * Record
==================== */

type records = Record<string, Person>

// type records = {
//     [x: string]: Person;
// }


/** ==================
 * Union
==================== */

/** Example */
type MixType = number | 'none' | 'all' | null

/* ----- Exclude ----- */

type MixTypeExclude = Exclude<MixType, number | 'all'>

// type MixTypeExclude = 'none' | null


/* ----- Extract ----- */

type MixTypeExtract = Extract<MixType, number | 'all' | 'x'>

// type MixTypeExtract = number | "all"


/* ----- NonNullable ----- */

type MixTypeNonNullable = NonNullable<MixType>  // removes undefined as well

// type MixTypeNonNullable = number | "none" | "all"


/** ==================
 * Function
==================== */

/** Example */
type FuncType = (this: boolean, name: string, maxAge: number) => boolean | null

/* ----- Parameters ----- */

type FuncTypeParameter = Parameters<FuncType>

// type FuncTypeParameter = [name: string, maxAge: number]


/* ----- ReturnType ----- */

type FuncTypeReturnType = ReturnType<FuncType>

// type FuncTypeReturnType = boolean | null


/* ----- ThisParameterType ----- */

type FuncTypeThisParameterType = ThisParameterType<FuncType>

// type FuncTypeThisParameterType = boolean


/* ----- OmitThisParameter ----- */

type FuncTypeOmitThisParameter = OmitThisParameter<FuncType>

// type FuncTypeOmitThisParameter = (name: string, maxAge: number) => boolean | null


/** ==================
 * String
==================== */

/** Example */
type StrType = 'hello' | 'Bye'

/* ----- Uppercase ----- */

type StrTypeUppercase = Uppercase<StrType>

// type StrTypeUppercase = "HELLO" | "BYE"


/* ----- Lowercase ----- */

type StrTypeLowercase = Lowercase<StrType>

// type StrTypeLowercase = "hello" | "bye"


/* ----- Capitalize ----- */

type StrTypeCapitalize = Capitalize<StrType>

// type StrTypeCapitalize = "Bye" | "Hello"


/* ----- Uncapitalize ----- */

type StrTypeUncapitalize = Uncapitalize<StrType>

// type StrTypeUncapitalize = "hello" | "bye"


/** ==================
 * JavaScript Global
==================== */

/* ---- ConstructorParameters ----- */

type ErrorConstructorParameters = ConstructorParameters<ErrorConstructor>

// type ErrorConstructorParameters = [message?: string | undefined]

type RegExpConstructorParameters = ConstructorParameters<RegExpConstructor>

// type RegExpConstructorParameters = [pattern: string | RegExp, flags?: string | undefined]


// TODO: InstanceType
// TODO: ThisType