@monstermann/fn/dist/array/mapAtOr.js

A utility library for TypeScript.

import { is } from "../function/is.js";
import { resolveOffset } from "./internals/offset.js";
import { dfdlT } from "@monstermann/dfdl";
import { cloneArray } from "@monstermann/remmi";

//#region src/array/mapAtOr.ts
/**
* `mapAtOr(array, index, mapper, fallback)`
*
* Applies the `mapper` function to the element at the specified `index` in `array`, returning a new array with the mapped element, or `fallback` if the index is out of bounds.
*
* ```ts
* mapAtOr([1, 2, 3], 10, (x) => x * 10, []); // []
* ```
*
* ```ts
* pipe(
*     [1, 2, 3],
*     mapAtOr(10, (x) => x * 10, []),
* ); // []
* ```
*/
const mapAtOr = dfdlT((target, idx, map, or) => {
	const offset = resolveOffset(target, idx);
	if (offset < 0) return or;
	const prev = target[offset];
	const next = map(prev, offset, target);
	if (is(prev, next)) return target;
	target = cloneArray(target);
	target.splice(offset, 1, next);
	return target;
}, 4);

//#endregion
export { mapAtOr };