type MapKey<BaseType> = BaseType extends Map<infer KeyType, unknown> ? KeyType : never; | |
type MapValue<BaseType> = BaseType extends Map<unknown, infer ValueType> ? ValueType : never; | |
export type ArrayEntry<BaseType extends readonly unknown[]> = [number, BaseType[number]]; | |
export type MapEntry<BaseType> = [MapKey<BaseType>, MapValue<BaseType>]; | |
export type ObjectEntry<BaseType> = [keyof BaseType, BaseType[keyof BaseType]]; | |
export type SetEntry<BaseType> = BaseType extends Set<infer ItemType> ? [ItemType, ItemType] : never; | |
/** | |
Many collections have an `entries` method which returns an array of a given object's own enumerable string-keyed property [key, value] pairs. The `Entry` type will return the type of that collection's entry. | |
For example the {@link https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/entries|`Object`}, {@link https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map/entries|`Map`}, {@link https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/entries|`Array`}, and {@link https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/entries|`Set`} collections all have this method. Note that `WeakMap` and `WeakSet` do not have this method since their entries are not enumerable. | |
@see `Entries` if you want to just access the type of the array of entries (which is the return of the `.entries()` method). | |
@example | |
``` | |
import type {Entry} from 'type-fest'; | |
interface Example { | |
someKey: number; | |
} | |
const manipulatesEntry = (example: Entry<Example>) => [ | |
// Does some arbitrary processing on the key (with type information available) | |
example[0].toUpperCase(), | |
// Does some arbitrary processing on the value (with type information available) | |
example[1].toFixed(), | |
]; | |
const example: Example = {someKey: 1}; | |
const entry = Object.entries(example)[0] as Entry<Example>; | |
const output = manipulatesEntry(entry); | |
// Objects | |
const objectExample = {a: 1}; | |
const objectEntry: Entry<typeof objectExample> = ['a', 1]; | |
// Arrays | |
const arrayExample = ['a', 1]; | |
const arrayEntryString: Entry<typeof arrayExample> = [0, 'a']; | |
const arrayEntryNumber: Entry<typeof arrayExample> = [1, 1]; | |
// Maps | |
const mapExample = new Map([['a', 1]]); | |
const mapEntry: Entry<typeof mapExample> = ['a', 1]; | |
// Sets | |
const setExample = new Set(['a', 1]); | |
const setEntryString: Entry<typeof setExample> = ['a', 'a']; | |
const setEntryNumber: Entry<typeof setExample> = [1, 1]; | |
``` | |
@category Object | |
@category Map | |
@category Array | |
@category Set | |
*/ | |
export type Entry<BaseType> = BaseType extends Map<unknown, unknown> | |
? MapEntry<BaseType> | |
: BaseType extends Set<unknown> | |
? SetEntry<BaseType> | |
: BaseType extends readonly unknown[] | |
? ArrayEntry<BaseType> | |
: BaseType extends object | |
? ObjectEntry<BaseType> | |
: never; | |