source: imaps-frontend/node_modules/core-js/internals/async-iterator-map.js

'use strict';
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 getIteratorDirect = require('../internals/get-iterator-direct');
var createAsyncIteratorProxy = require('../internals/async-iterator-create-proxy');
var createIterResultObject = require('../internals/create-iter-result-object');
var closeAsyncIteration = require('../internals/async-iterator-close');

var AsyncIteratorProxy = createAsyncIteratorProxy(function (Promise) {
  var state = this;
  var iterator = state.iterator;
  var mapper = state.mapper;

  return new Promise(function (resolve, reject) {
    var doneAndReject = function (error) {
      state.done = true;
      reject(error);
    };

    var ifAbruptCloseAsyncIterator = function (error) {
      closeAsyncIteration(iterator, doneAndReject, error, doneAndReject);
    };

    Promise.resolve(anObject(call(state.next, iterator))).then(function (step) {
      try {
        if (anObject(step).done) {
          state.done = true;
          resolve(createIterResultObject(undefined, true));
        } else {
          var value = step.value;
          try {
            var result = mapper(value, state.counter++);

            var handler = function (mapped) {
              resolve(createIterResultObject(mapped, false));
            };

            if (isObject(result)) Promise.resolve(result).then(handler, ifAbruptCloseAsyncIterator);
            else handler(result);
          } catch (error2) { ifAbruptCloseAsyncIterator(error2); }
        }
      } catch (error) { doneAndReject(error); }
    }, doneAndReject);
  });
});

// `AsyncIterator.prototype.map` method
// https://github.com/tc39/proposal-iterator-helpers
module.exports = function map(mapper) {
  anObject(this);
  aCallable(mapper);
  return new AsyncIteratorProxy(getIteratorDirect(this), {
    mapper: mapper
  });
};