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

A utility library for TypeScript.

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

//#region src/array/flatMap.ts
/**
* `flatMap(array, mapper)`
*
* Maps each element in `array` using the `mapper` function and flattens the result by one level.
*
* ```ts
* flatMap([1, 2, 3], (x) => [x, x * 2]); // [1, 2, 2, 4, 3, 6]
* ```
*
* ```ts
* pipe(
*     [1, 2, 3],
*     flatMap((x) => [x, x * 2]),
* ); // [1, 2, 2, 4, 3, 6]
* ```
*/
const flatMap = dfdlT((target, mapper) => {
	let hasChanges = false;
	const result = target.flatMap((a, b, c) => {
		const output = mapper(a, b, c);
		hasChanges ||= !(output.length === 1 && is(output[0], a));
		return output;
	});
	return hasChanges ? markAsMutable(result) : target;
}, 2);

//#endregion
export { flatMap };