@monstermann/fn/dist/array/mapAt.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/mapAt.ts
/**
* `mapAt(array, index, mapper)`
*
* Applies the `mapper` function to the element at the specified `index` in `array`, returning a new array with the mapped element.
*
* ```ts
* mapAt([1, 2, 3, 4], 1, (x) => x * 10); // [1, 20, 3, 4]
* ```
*
* ```ts
* pipe(
*     [1, 2, 3, 4],
*     mapAt(1, (x) => x * 10),
* ); // [1, 20, 3, 4]
* ```
*/
const mapAt = dfdlT((target, idx, map) => {
	const offset = resolveOffset(target, idx);
	if (offset < 0) return target;
	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;
}, 3);

//#endregion
export { mapAt };