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PrimitiveType ​

The primitive types including number, string, boolean, undefined, null, bigint, and symbol

Added in v0.0.1

Source ​

typescript
export type PrimitiveType =
  | undefined
  | null
  | number
  | string
  | boolean
  | bigint
  | symbol

NumberString ​

A string composed of numbers.

Added in v0.0.1

Source ​

typescript
export type NumberString = `${number}`

ObjectLike ​

Non-function object.

Added in v0.0.1

Source ​

typescript
export type ObjectLike = object & { call?: never; [x: PropertyKey]: any }

ExtractUnion ​

Extract a union type from a tuple.

Added in v0.0.1

Source ​

typescript
export type ExtractUnion<T extends readonly string[]> = {
  [K in keyof T]: T[K]
}[number]

KeyOrIndex ​

Extracts a number from a string in the form of [${number}] or ${number}. Otherwise, returns the original string.

Added in v0.0.1

Source ​

typescript
export type KeyOrIndex<T extends string> = T extends
  | `[${infer D extends number}]`
  | `${infer D extends number}`
  ? D
  : T

Tail ​

Returns the last element of tuple type.

Added in v0.0.1

Source ​

typescript
export type Tail<T extends readonly any[]> = T extends readonly [
  ...any[],
  infer L
]
  ? L
  : never

Head ​

Returns the first element of tuple type.

Added in v0.0.1

Source ​

typescript
export type Head<T extends readonly any[]> = T extends readonly [
  infer L,
  ...any[]
]
  ? L
  : never

Edge ​

Retrieve the first or last element of tuple T, determined by type D.

Added in v0.0.1

Source ​

typescript
export type Edge<
  T extends readonly any[],
  D = 'left' | 'right'
> = D extends 'left' ? Head<T> : Tail<T>

EdgeReverse ​

Similar to Edge, but the effects of 'left' and 'right' for D are reversed.

Added in v0.0.1

Source ​

typescript
export type EdgeReverse<
  T extends readonly any[],
  D = 'left' | 'right'
> = D extends 'right' ? Head<T> : Tail<T>

EmptyOrParameters ​

Returns the parameter types of the function; if the input is not a function, returns the never[] type.

Added in v0.0.1

Source ​

typescript
export type EmptyOrParameters<T> = T extends (...args: any[]) => any
  ? Parameters<T>
  : never[]

EmptyOrReturnType ​

Returns the return type of the function; if the input is not a function, returns the void type.

Added in v0.0.1

Source ​

typescript
export type EmptyOrReturnType<T> = T extends (...args: any[]) => any
  ? ReturnType<T>
  : void

WithFallback ​

Either returns the result of type T or a fallback value R if the result is null or undefined.

Added in v0.0.2

Source ​

typescript
export type WithFallback<T extends (...args: any[]) => any, R> =
  ReturnType<T> extends undefined | null ? R : ReturnType<T>

LiteralStringWithFallback ​

This type provides a default string value R when string type T is too general (like string).

It ensures type safety while allowing flexibility in scenarios such as configuration objects or optional parameters.

Added in v0.0.2

Source ​

typescript
export type LiteralStringWithFallback<T extends string, R extends string> = T &
  R extends never
  ? T
  : R

MappedTypeByKeyOrIndex ​

Generates plain objects or arrays based on input string/numeric index T, pointing to type V, with optionality controlled by type O.

Added in v0.0.2

Source ​

typescript
export type MappedTypeByKeyOrIndex<
  T extends string,
  V,
  O extends boolean = false
> =
  KeyOrIndex<T> extends string
    ? O extends false
      ? { [P in T]: V }
      : { [P in T]?: V }
    : O extends false
      ? unknown[] & { [P in KeyOrIndex<T>]: V }
      : unknown[] & { [P in KeyOrIndex<T>]?: V }

DeepMappedTypeByKeyOrIndex ​

Recursively parses the field path T and creates nested plain objects or arrays. It can interpret nested path strings like "data.[0].name", with the path's end field pointing to value V. O decides if the value is optional.

It is very useful for creating complex nested types based on string templates.

Added in v0.0.2

Source ​

typescript
export type DeepMappedTypeByKeyOrIndex<
  T extends string,
  V,
  O extends boolean = false
> = T extends `[${infer Key extends number}][${infer Rest}`
  ? MappedTypeByKeyOrIndex<`${Key}`, DeepMappedTypeByKeyOrIndex<`[${Rest}`, V>>
  : T extends `${infer Key}[${infer Rest}`
    ? MappedTypeByKeyOrIndex<
        `${Key}`,
        DeepMappedTypeByKeyOrIndex<`[${Rest}`, V>
      >
    : T extends `[${infer Key extends number}].${infer Rest}`
      ? MappedTypeByKeyOrIndex<`${Key}`, DeepMappedTypeByKeyOrIndex<Rest, V>>
      : T extends `${infer Key}.${infer Rest}`
        ? MappedTypeByKeyOrIndex<`${Key}`, DeepMappedTypeByKeyOrIndex<Rest, V>>
        : MappedTypeByKeyOrIndex<T, V, O>

DataUnit ​

DataUnit type represents different units of digital data.

Added in v0.0.2

Source ​

typescript
export type DataUnit =
  | 'bit'
  | 'B'
  | 'KB'
  | 'MB'
  | 'GB'
  | 'TB'
  | 'PB'
  | 'EB'
  | 'ZB'
  | 'YB'