JavaScript新功能介绍之findLast()和findLastIndex()

const array = [{v: 1}, {v: 2}, {v: 3}, {v: 4}, {v: 5}];

array.find(elem => elem.v > 3); // {v: 4}
array.findIndex(elem => elem.v > 3); // 3

const array = [{v: 1}, {v: 2}, {v: 3}, {v: 4}, {v: 5}];

array.findLast(elem => elem.v > 3); // {v: 5}
array.findLastIndex(elem => elem.v > 3); // 4
array.findLastIndex(elem => elem.v > 5); // -1

function findLast(arr, callback, thisArg) {
  for (let index = arr.length - 1; index >= 0; index--) {
    const value = arr[index];
    if (callback.call(thisArg, value, index, arr)) {
      return value;
    }
  }
  return undefined;
}

const array = [{v: 1}, {v: 2}, {v: 3}, {v: 4}, {v: 5}];
findLast(array, elem => elem.v > 3, array) // {v: 5}
findLast(array, elem => elem.v > 5, array) // -1

function findLastIndex(arr, callback, thisArg) {
  for (let index = arr.length - 1; index >= 0; index--) {
    const value = arr[index];
    if (callback.call(thisArg, value, index, arr)) {
      return index;
    }
  }
  return -1;
}

const array = [{v: 1}, {v: 2}, {v: 3}, {v: 4}, {v: 5}];
findLastIndex(array, elem => elem.v > 3, array) // 4
findLastIndex(array, elem => elem.v > 5, array) // -1

import findLastIndex from './findLastIndex.js'
import isArrayLike from './isArrayLike.js'

/**
 * This method is like `find` except that it iterates over elements of
 * `collection` from right to left.
 *
 * @since 2.0.0
 * @category Collection
 * @param {Array|Object} collection The collection to inspect.
 * @param {Function} predicate The function invoked per iteration.
 * @param {number} [fromIndex=collection.length-1] The index to search from.
 * @returns {*} Returns the matched element, else `undefined`.
 * @see find, findIndex, findKey, findLastIndex, findLastKey
 * @example
 *
 * findLast([1, 2, 3, 4], n => n % 2 == 1)
 * // => 3
 */
function findLast(collection, predicate, fromIndex) {
  let iteratee
  const iterable = Object(collection)
  if (!isArrayLike(collection)) {
    collection = Object.keys(collection)
    iteratee = predicate
    predicate = (key) => iteratee(iterable[key], key, iterable)
  }
  const index = findLastIndex(collection, predicate, fromIndex)
  return index > -1 ? iterable[iteratee ? collection[index] : index] : undefined
}

export default findLast

import baseFindIndex from './.internal/baseFindIndex.js'
import toInteger from './toInteger.js'

/**
 * This method is like `findIndex` except that it iterates over elements
 * of `collection` from right to left.
 *
 * @since 2.0.0
 * @category Array
 * @param {Array} array The array to inspect.
 * @param {Function} predicate The function invoked per iteration.
 * @param {number} [fromIndex=array.length-1] The index to search from.
 * @returns {number} Returns the index of the found element, else `-1`.
 * @see find, findIndex, findKey, findLast, findLastKey
 * @example
 *
 * const users = [
 *   { 'user': 'barney',  'active': true },
 *   { 'user': 'fred',    'active': false },
 *   { 'user': 'pebbles', 'active': false }
 * ]
 *
 * findLastIndex(users, ({ user }) => user == 'pebbles')
 * // => 2
 */
function findLastIndex(array, predicate, fromIndex) {
  const length = array == null ? 0 : array.length
  if (!length) {
    return -1
  }
  let index = length - 1
  if (fromIndex !== undefined) {
    index = toInteger(fromIndex)
    index = fromIndex < 0
      ? Math.max(length + index, 0)
      : Math.min(index, length - 1)
  }
  return baseFindIndex(array, predicate, index, true)
}

export default findLastIndex