lodash collection flatMapDeep 활용

import baseFlatten from './.internal/baseFlatten.js'
import map from './map.js'

/**
 * This method is like `flatMap` except that it recursively flattens the
 * mapped results up to `depth` times.
 *
 * @since 4.7.0
 * @category Collection
 * @param {Array|Object} collection The collection to iterate over.
 * @param {Function} iteratee The function invoked per iteration.
 * @param {number} [depth=1] The maximum recursion depth.
 * @returns {Array} Returns the new flattened array.
 * @see flatMap, flatMapDeep, flatten, flattenDeep, flattenDepth, map, mapKeys, mapValues
 * @example
 *
 * function duplicate(n) {
 *   return [[[n, n]]]
 * }
 *
 * flatMapDepth([1, 2], duplicate, 2)
 * // => [[1, 1], [2, 2]]
 */
function flatMapDepth(collection, iteratee, depth) {
  depth = depth === undefined ? 1 : +depth
  return baseFlatten(map(collection, iteratee), depth)
}

export default flatMapDepth

import isFlattenable from './isFlattenable.js'

/**
 * The base implementation of `flatten` with support for restricting flattening.
 *
 * @private
 * @param {Array} array The array to flatten.
 * @param {number} depth The maximum recursion depth.
 * @param {boolean} [predicate=isFlattenable] The function invoked per iteration.
 * @param {boolean} [isStrict] Restrict to values that pass `predicate` checks.
 * @param {Array} [result=[]] The initial result value.
 * @returns {Array} Returns the new flattened array.
 */
function baseFlatten(array, depth, predicate, isStrict, result) {
  predicate || (predicate = isFlattenable)
  result || (result = [])

  if (array == null) {
    return result
  }

  for (const value of array) {
    if (depth > 0 && predicate(value)) {
      if (depth > 1) {
        // Recursively flatten arrays (susceptible to call stack limits).
        baseFlatten(value, depth - 1, predicate, isStrict, result)
      } else {
        result.push(...value)
      }
    } else if (!isStrict) {
      result[result.length] = value
    }
  }
  return result
}

export default baseFlatten