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

A utility library for TypeScript.

import { dfdlT } from "@monstermann/dfdl";
import { cloneMap } from "@monstermann/remmi";

//#region src/map/filter.ts
/**
* `filter(map, predicate)`
*
* Filters `map` by keeping only the entries where `predicate` returns true for the value.
*
* ```ts
* filter(
*     new Map([
*         ["a", 1],
*         ["b", 2],
*         ["c", 3],
*     ]),
*     (value) => value > 1,
* ); // Map(2) { "b" => 2, "c" => 3 }
* ```
*
* ```ts
* pipe(
*     new Map([
*         ["a", 1],
*         ["b", 2],
*         ["c", 3],
*     ]),
*     filter((value) => value > 1),
* ); // Map(2) { "b" => 2, "c" => 3 }
* ```
*/
const filter = dfdlT((target, predicate) => {
	let result;
	for (const [key, value] of target) if (!predicate(value, key, target)) {
		result ??= cloneMap(target);
		result.delete(key);
	}
	return result ?? target;
}, 2);

//#endregion
export { filter };