source: frontend/node_modules/core-js/internals/flatten-into-array.js

'use strict';
var isArray = require('../internals/is-array');
var lengthOfArrayLike = require('../internals/length-of-array-like');
var doesNotExceedSafeInteger = require('../internals/does-not-exceed-safe-integer');
var bind = require('../internals/function-bind-context');
var createProperty = require('../internals/create-property');

// `FlattenIntoArray` abstract operation
// https://tc39.es/ecma262/#sec-flattenintoarray
var flattenIntoArray = function (target, original, source, sourceLen, start, depth, mapper, thisArg) {
  var targetIndex = start;
  var sourceIndex = 0;
  var mapFn = mapper ? bind(mapper, thisArg) : false;
  var element, elementLen;

  while (sourceIndex < sourceLen) {
    if (sourceIndex in source) {
      element = mapFn ? mapFn(source[sourceIndex], sourceIndex, original) : source[sourceIndex];

      if (depth > 0 && isArray(element)) {
        elementLen = lengthOfArrayLike(element);
        targetIndex = flattenIntoArray(target, original, element, elementLen, targetIndex, depth - 1) - 1;
      } else {
        doesNotExceedSafeInteger(targetIndex + 1);
        createProperty(target, targetIndex, element);
      }

      targetIndex++;
    }
    sourceIndex++;
  }
  return targetIndex;
};

module.exports = flattenIntoArray;