source: node_modules/core-js-pure/internals/async-iterator-create-proxy.js

'use strict';
var call = require('../internals/function-call');
var perform = require('../internals/perform');
var anObject = require('../internals/an-object');
var create = require('../internals/object-create');
var createNonEnumerableProperty = require('../internals/create-non-enumerable-property');
var defineBuiltIns = require('../internals/define-built-ins');
var wellKnownSymbol = require('../internals/well-known-symbol');
var InternalStateModule = require('../internals/internal-state');
var getBuiltIn = require('../internals/get-built-in');
var getMethod = require('../internals/get-method');
var AsyncIteratorPrototype = require('../internals/async-iterator-prototype');
var createIterResultObject = require('../internals/create-iter-result-object');
var iteratorClose = require('../internals/iterator-close');

var Promise = getBuiltIn('Promise');

var TO_STRING_TAG = wellKnownSymbol('toStringTag');
var ASYNC_ITERATOR_HELPER = 'AsyncIteratorHelper';
var WRAP_FOR_VALID_ASYNC_ITERATOR = 'WrapForValidAsyncIterator';
var setInternalState = InternalStateModule.set;

var createAsyncIteratorProxyPrototype = function (IS_ITERATOR) {
  var IS_GENERATOR = !IS_ITERATOR;
  var getInternalState = InternalStateModule.getterFor(IS_ITERATOR ? WRAP_FOR_VALID_ASYNC_ITERATOR : ASYNC_ITERATOR_HELPER);

  var getStateOrEarlyExit = function (that) {
    var stateCompletion = perform(function () {
      return getInternalState(that);
    });

    var stateError = stateCompletion.error;
    var state = stateCompletion.value;

    if (stateError || (IS_GENERATOR && state.done)) {
      return { exit: true, value: stateError ? Promise.reject(state) : Promise.resolve(createIterResultObject(undefined, true)) };
    } return { exit: false, value: state };
  };

  return defineBuiltIns(create(AsyncIteratorPrototype), {
    next: function next() {
      var stateCompletion = getStateOrEarlyExit(this);
      var state = stateCompletion.value;
      if (stateCompletion.exit) return state;
      var handlerCompletion = perform(function () {
        return anObject(state.nextHandler(Promise));
      });
      var handlerError = handlerCompletion.error;
      var value = handlerCompletion.value;
      if (handlerError) state.done = true;
      return handlerError ? Promise.reject(value) : Promise.resolve(value);
    },
    'return': function () {
      var stateCompletion = getStateOrEarlyExit(this);
      var state = stateCompletion.value;
      if (stateCompletion.exit) return state;
      state.done = true;
      var iterator = state.iterator;
      var returnMethod, result;
      var completion = perform(function () {
        if (state.inner) try {
          iteratorClose(state.inner.iterator, 'normal');
        } catch (error) {
          return iteratorClose(iterator, 'throw', error);
        }
        return getMethod(iterator, 'return');
      });
      returnMethod = result = completion.value;
      if (completion.error) return Promise.reject(result);
      if (returnMethod === undefined) return Promise.resolve(createIterResultObject(undefined, true));
      completion = perform(function () {
        return call(returnMethod, iterator);
      });
      result = completion.value;
      if (completion.error) return Promise.reject(result);
      return IS_ITERATOR ? Promise.resolve(result) : Promise.resolve(result).then(function (resolved) {
        anObject(resolved);
        return createIterResultObject(undefined, true);
      });
    }
  });
};

var WrapForValidAsyncIteratorPrototype = createAsyncIteratorProxyPrototype(true);
var AsyncIteratorHelperPrototype = createAsyncIteratorProxyPrototype(false);

createNonEnumerableProperty(AsyncIteratorHelperPrototype, TO_STRING_TAG, 'Async Iterator Helper');

module.exports = function (nextHandler, IS_ITERATOR) {
  var AsyncIteratorProxy = function AsyncIterator(record, state) {
    if (state) {
      state.iterator = record.iterator;
      state.next = record.next;
    } else state = record;
    state.type = IS_ITERATOR ? WRAP_FOR_VALID_ASYNC_ITERATOR : ASYNC_ITERATOR_HELPER;
    state.nextHandler = nextHandler;
    state.counter = 0;
    state.done = false;
    setInternalState(this, state);
  };

  AsyncIteratorProxy.prototype = IS_ITERATOR ? WrapForValidAsyncIteratorPrototype : AsyncIteratorHelperPrototype;

  return AsyncIteratorProxy;
};