source: node_modules/core-js-pure/modules/esnext.async-iterator.reduce.js

'use strict';
var $ = require('../internals/export');
var call = require('../internals/function-call');
var aCallable = require('../internals/a-callable');
var anObject = require('../internals/an-object');
var isObject = require('../internals/is-object');
var getBuiltIn = require('../internals/get-built-in');
var getIteratorDirect = require('../internals/get-iterator-direct');
var closeAsyncIteration = require('../internals/async-iterator-close');

var Promise = getBuiltIn('Promise');
var $TypeError = TypeError;

// `AsyncIterator.prototype.reduce` method
// https://github.com/tc39/proposal-async-iterator-helpers
$({ target: 'AsyncIterator', proto: true, real: true }, {
  reduce: function reduce(reducer /* , initialValue */) {
    anObject(this);
    aCallable(reducer);
    var record = getIteratorDirect(this);
    var iterator = record.iterator;
    var next = record.next;
    var noInitial = arguments.length < 2;
    var accumulator = noInitial ? undefined : arguments[1];
    var counter = 0;

    return new Promise(function (resolve, reject) {
      var ifAbruptCloseAsyncIterator = function (error) {
        closeAsyncIteration(iterator, reject, error, reject);
      };

      var loop = function () {
        try {
          Promise.resolve(anObject(call(next, iterator))).then(function (step) {
            try {
              if (anObject(step).done) {
                noInitial ? reject(new $TypeError('Reduce of empty iterator with no initial value')) : resolve(accumulator);
              } else {
                var value = step.value;
                if (noInitial) {
                  noInitial = false;
                  accumulator = value;
                  loop();
                } else try {
                  var result = reducer(accumulator, value, counter);

                  var handler = function ($result) {
                    accumulator = $result;
                    loop();
                  };

                  if (isObject(result)) Promise.resolve(result).then(handler, ifAbruptCloseAsyncIterator);
                  else handler(result);
                } catch (error3) { ifAbruptCloseAsyncIterator(error3); }
              }
              counter++;
            } catch (error2) { reject(error2); }
          }, reject);
        } catch (error) { reject(error); }
      };

      loop();
    });
  }
});