es-toolkit/dist/array/keyBy.js

A state-of-the-art, high-performance JavaScript utility library with a small bundle size and strong type annotations.

//#region src/array/keyBy.ts
/**
* Maps each element of an array based on a provided key-generating function.
*
* This function takes an array and a function that generates a key from each element. It returns
* an object where the keys are the generated keys and the values are the corresponding elements.
* If there are multiple elements generating the same key, the last element among them is used
* as the value.
*
* @template T - The type of elements in the array.
* @template K - The type of keys.
* @param arr - The array of elements to be mapped.
* @param getKeyFromItem - A function that generates a key from an element, its index, and the array.
* @returns An object where keys are mapped to each element of an array.
*
* @example
* const array = [
*   { category: 'fruit', name: 'apple' },
*   { category: 'fruit', name: 'banana' },
*   { category: 'vegetable', name: 'carrot' }
* ];
* const result = keyBy(array, item => item.category);
* // result will be:
* // {
* //   fruit: { category: 'fruit', name: 'banana' },
* //   vegetable: { category: 'vegetable', name: 'carrot' }
* // }
*
* @example
* // Using index parameter
* const items = ['a', 'b', 'c'];
* const result = keyBy(items, (item, index) => index);
* // result will be: { 0: 'a', 1: 'b', 2: 'c' }
*/
function keyBy(arr, getKeyFromItem) {
	const result = {};
	for (let i = 0; i < arr.length; i++) {
		const item = arr[i];
		const key = getKeyFromItem(item, i, arr);
		result[key] = item;
	}
	return result;
}
//#endregion
exports.keyBy = keyBy;