source: frontend/node_modules/core-js/internals/iterate.js

'use strict';
var bind = require('../internals/function-bind-context');
var call = require('../internals/function-call');
var anObject = require('../internals/an-object');
var tryToString = require('../internals/try-to-string');
var isArrayIteratorMethod = require('../internals/is-array-iterator-method');
var lengthOfArrayLike = require('../internals/length-of-array-like');
var isPrototypeOf = require('../internals/object-is-prototype-of');
var getIterator = require('../internals/get-iterator');
var getIteratorMethod = require('../internals/get-iterator-method');
var iteratorClose = require('../internals/iterator-close');

var $TypeError = TypeError;

var Result = function (stopped, result) {
  this.stopped = stopped;
  this.result = result;
};

var ResultPrototype = Result.prototype;

module.exports = function (iterable, unboundFunction, options) {
  var that = options && options.that;
  var AS_ENTRIES = !!(options && options.AS_ENTRIES);
  var IS_RECORD = !!(options && options.IS_RECORD);
  var IS_ITERATOR = !!(options && options.IS_ITERATOR);
  var INTERRUPTED = !!(options && options.INTERRUPTED);
  var fn = bind(unboundFunction, that);
  var iterator, iterFn, index, length, result, next, step;

  var stop = function (condition) {
    var $iterator = iterator;
    iterator = undefined;
    if ($iterator) iteratorClose($iterator, 'normal');
    return new Result(true, condition);
  };

  var callFn = function (value) {
    if (AS_ENTRIES) {
      anObject(value);
      return INTERRUPTED ? fn(value[0], value[1], stop) : fn(value[0], value[1]);
    } return INTERRUPTED ? fn(value, stop) : fn(value);
  };

  if (IS_RECORD) {
    iterator = iterable.iterator;
  } else if (IS_ITERATOR) {
    iterator = iterable;
  } else {
    iterFn = getIteratorMethod(iterable);
    if (!iterFn) throw new $TypeError(tryToString(iterable) + ' is not iterable');
    // optimisation for array iterators
    if (isArrayIteratorMethod(iterFn)) {
      for (index = 0, length = lengthOfArrayLike(iterable); length > index; index++) {
        result = callFn(iterable[index]);
        if (result && isPrototypeOf(ResultPrototype, result)) return result;
      } return new Result(false);
    }
    iterator = getIterator(iterable, iterFn);
  }

  next = IS_RECORD ? iterable.next : iterator.next;
  while (!(step = call(next, iterator)).done) {
    // `IteratorValue` errors should propagate without closing the iterator
    var value = step.value;
    try {
      result = callFn(value);
    } catch (error) {
      if (iterator) iteratorClose(iterator, 'throw', error);
      else throw error;
    }
    if (typeof result == 'object' && result && isPrototypeOf(ResultPrototype, result)) return result;
  } return new Result(false);
};