@monstermann/fn/dist/map/mapOrElse.js

A utility library for TypeScript.

import { is } from "../function/is.js";
import { dfdlT } from "@monstermann/dfdl";
import { cloneMap } from "@monstermann/remmi";

//#region src/map/mapOrElse.ts
/**
* `mapOrElse(map, key, transform, orElse)`
*
* Transforms the value at `key` in `map` using `transform`, calling `orElse` with the map if the key doesn't exist.
*
* ```ts
* mapOrElse(
*     new Map([
*         ["a", 1],
*         ["b", 2],
*     ]),
*     "a",
*     (value) => value * 2,
*     () => null,
* ); // Map(2) { "a" => 2, "b" => 2 }
*
* mapOrElse(
*     new Map([
*         ["a", 1],
*         ["b", 2],
*     ]),
*     "c",
*     (value) => value * 2,
*     (map) => map.size,
* ); // 2
* ```
*
* ```ts
* pipe(
*     new Map([
*         ["a", 1],
*         ["b", 2],
*     ]),
*     mapOrElse(
*         "a",
*         (value) => value * 2,
*         () => null,
*     ),
* ); // Map(2) { "a" => 2, "b" => 2 }
*
* pipe(
*     new Map([
*         ["a", 1],
*         ["b", 2],
*     ]),
*     mapOrElse(
*         "c",
*         (value) => value * 2,
*         (map) => map.size,
*     ),
* ); // 2
* ```
*/
const mapOrElse = dfdlT((target, key, transform, orElse) => {
	if (!target.has(key)) return orElse(target);
	const prev = target.get(key);
	const next = transform(prev, key, target);
	if (is(prev, next)) return target;
	const result = cloneMap(target);
	result.set(key, next);
	return result;
}, 4);

//#endregion
export { mapOrElse };