Usage

isMap(new Map()); // => true
isMap(new Set()); // => false

Installation

CLI

npx atmx add helper is-map

Manually

Copy and paste the following method into @/utils/helpers/undefined.ts:

import { isTagged } from "@/helpers/is-tagged.ts";

import type { StrictExtract } from "@/types/strict-extract.ts";

/**
* Return true if the given value is a Map.
*
* Instances from [other realms][1] are also supported.
*
* [1]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/instanceof#instanceof_and_multiple_realms
*
* @example
* isMap(new Map()) // => true
* isMap(new Set()) // => false
*/
export function isMap<Input>(value: Input): value is ExtractMap<Input> {
return isTagged(value, "[object Map]");
}

/**
* An absurdly complicated but accurate type for extracting Map types.
*
* It's like `Extract<T, Map<any, any>>` but better with edge cases.
*/
export type ExtractMap<T> = T extends any
? [StrictExtract<T, ReadonlyMap<unknown, unknown>>] extends [
  ReadonlyMap<unknown, unknown>,
]
? Extract<T, ReadonlyMap<unknown, unknown>>
: [StrictExtract<T, Map<unknown, unknown>>] extends [Map<unknown, unknown>]
  ? Extract<T, Map<unknown, unknown>>
  : Map<unknown, unknown> extends T
    ? Map<unknown, unknown>
    : never
: never;