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

A utility library for TypeScript.

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

//#region src/map/mapOrThrow.ts
/**
* `mapOrThrow(map, key, transform)`
*
* Transforms the value at `key` in `map` using `transform`, throwing an error if the key doesn't exist.
*
* ```ts
* mapOrThrow(
*     new Map([
*         ["a", 1],
*         ["b", 2],
*     ]),
*     "a",
*     (value) => value * 2,
* ); // Map(2) { "a" => 2, "b" => 2 }
*
* mapOrThrow(
*     new Map([
*         ["a", 1],
*         ["b", 2],
*     ]),
*     "c",
*     (value) => value * 2,
* ); // throws FnError
* ```
*
* ```ts
* pipe(
*     new Map([
*         ["a", 1],
*         ["b", 2],
*     ]),
*     mapOrThrow("a", (value) => value * 2),
* ); // Map(2) { "a" => 2, "b" => 2 }
*
* pipe(
*     new Map([
*         ["a", 1],
*         ["b", 2],
*     ]),
*     mapOrThrow("c", (value) => value * 2),
* ); // throws FnError
* ```
*/
const mapOrThrow = dfdlT((target, key, transform) => {
	if (!target.has(key)) throw new FnError("Map.mapOrThrow: Key does not exist.", [
		target,
		key,
		transform
	]);
	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;
}, 3);

//#endregion
export { mapOrThrow };