es-toolkit/dist/array/intersectionBy.js

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

//#region src/array/intersectionBy.ts
/**
* Returns the intersection of two arrays based on a mapping function.
*
* This function takes two arrays and a mapping function. It returns a new array containing
* the elements from the first array that, when mapped using the provided function, have matching
* mapped elements in the second array. It effectively filters out any elements from the first array
* that do not have corresponding mapped values in the second array.
*
* @template T - The type of elements in the first array.
* @template U - The type of elements in the second array.
* @param firstArr - The first array to compare.
* @param secondArr - The second array to compare.
* @param mapper - A function to map the elements of both arrays for comparison.
* @returns A new array containing the elements from the first array that have corresponding mapped values in the second array.
*
* @example
* const array1 = [{ id: 1 }, { id: 2 }, { id: 3 }];
* const array2 = [{ id: 2 }, { id: 4 }];
* const mapper = item => item.id;
* const result = intersectionBy(array1, array2, mapper);
* // result will be [{ id: 2 }] since only this element has a matching id in both arrays.
*
* @example
* const array1 = [
*   { id: 1, name: 'jane' },
*   { id: 2, name: 'amy' },
*   { id: 3, name: 'michael' },
* ];
* const array2 = [2, 4];
* const mapper = item => (typeof item === 'object' ? item.id : item);
* const result = intersectionBy(array1, array2, mapper);
* // result will be [{ id: 2, name: 'amy' }] since only this element has a matching id that is equal to seconds array's element.
*/
function intersectionBy(firstArr, secondArr, mapper) {
	const result = [];
	const mappedSecondSet = new Set(secondArr.map(mapper));
	for (let i = 0; i < firstArr.length; i++) {
		const item = firstArr[i];
		const mappedItem = mapper(item);
		if (mappedSecondSet.has(mappedItem)) {
			result.push(item);
			mappedSecondSet.delete(mappedItem);
		}
	}
	return result;
}
//#endregion
exports.intersectionBy = intersectionBy;