es-toolkit/dist/map/keyBy.js

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

//#region src/map/keyBy.ts
/**
* Maps each entry of a Map based on a provided key-generating function.
*
* This function takes a Map and a function that generates a key from each value-key pair.
* It returns a new Map where the keys are generated by the key function and the values are
* the corresponding values from the original map. If multiple entries produce the same key,
* the last value encountered will be used.
*
* @template K - The type of keys in the original Map.
* @template V - The type of values in the original Map.
* @template K2 - The type of keys to produce in the returned Map.
* @param map - The map of entries to be mapped.
* @param getKeyFromEntry - A function that generates a key from a value-key pair.
* @returns A Map where the generated keys are mapped to each entry's value.
*
* @example
* const map = new Map([
*   ['x', { type: 'fruit', name: 'apple' }],
*   ['y', { type: 'fruit', name: 'banana' }],
*   ['z', { type: 'vegetable', name: 'carrot' }]
* ]);
* const result = keyBy(map, item => item.type);
* // result will be:
* // Map(2) {
* //   'fruit' => { type: 'fruit', name: 'banana' },
* //   'vegetable' => { type: 'vegetable', name: 'carrot' }
* // }
*/
function keyBy(map, getKeyFromEntry) {
	const result = /* @__PURE__ */ new Map();
	for (const [key, value] of map) {
		const newKey = getKeyFromEntry(value, key, map);
		result.set(newKey, value);
	}
	return result;
}
//#endregion
exports.keyBy = keyBy;