require babel-polyfill and babel-core statements are preceded by asycn runtime code. plugin[babel-plugin-transform-async-to-generator]

[devarsh]

Input Code

require("babel-core/register")
require("babel-polyfill")

var fetch = require('isomorphic-fetch')

function fetchReddit(topic) {
  const redditUrl= `https://www.reddit.com/r/${topic}.json`
  return new Promise((resolve,reject) => {
    fetch(redditUrl).then(response => response.json()).then(result => resolve(result.data.children))
  })
}

async function read(topic) {
  var json = await fetchReddit(topic)
  console.log(json)
}

read('home')

Babel Configuration (.bablerc, package.json, cli command)

.babelrc

{
  "presets": ["es2015", "es2016", "es2017", "stage-2"],
}

package.json

devDependencies": {
   "babel": "^6.5.2",
    "babel-cli": "^6.11.4",
    "babel-core": "^6.10.4",
    "babel-eslint": "^6.1.0",
    "babel-plugin-transform-async-to-generator": "^6.8.0",
    "babel-preset-es2015": "^6.9.0",
    "babel-preset-es2016": "^6.11.3",
    "babel-preset-es2017": "^6.14.0",
    "babel-preset-stage-0": "^6.5.0",
    "babel-register": "^6.11.6",
    "isomorphic-fetch": "^2.2.1",
}

Current Behavior

The read function preceeds the require statement, which will result in undefined regeneratorRuntime

"use strict";

var read = function () {
  var _ref = _asyncToGenerator(regeneratorRuntime.mark(function _callee(topic) {
    var json;
    return regeneratorRuntime.wrap(function _callee$(_context) {
      while (1) {
        switch (_context.prev = _context.next) {
          case 0:
            _context.next = 2;
            return fetchReddit(topic);

          case 2:
            json = _context.sent;

            console.log(json);

          case 4:
          case "end":
            return _context.stop();
        }
      }
    }, _callee, this);
  }));

  return function read(_x) {
    return _ref.apply(this, arguments);
  };
}();

function _asyncToGenerator(fn) { return function () { var gen = fn.apply(this, arguments); return new Promise(function (resolve, reject) { function step(key, arg) { try { var info = gen[key](arg); var value = info.value; } catch (error) { reject(error); return; } if (info.done) { resolve(value); } else { return Promise.resolve(value).then(function (value) { return step("next", value); }, function (err) { return step("throw", err); }); } } return step("next"); }); }; }

require("babel-core/register");
require("babel-polyfill");

var fetch = require('isomorphic-fetch');

function fetchReddit(topic) {
  var redditUrl = "https://www.reddit.com/r/" + topic + ".json";
  return new Promise(function (resolve, reject) {
    fetch(redditUrl).then(function (response) {
      return response.json();
    }).then(function (result) {
      return resolve(result.data.children);
    });
  });
}

read('home');

Expected Behavior

"use strict";


require("babel-core/register");
require("babel-polyfill");
/* everthing else after the require statement */
var read = function () {
  var _ref = _asyncToGenerator(regeneratorRuntime.mark(function _callee(topic) {
    var json;
    return regeneratorRuntime.wrap(function _callee$(_context) {
      while (1) {
        switch (_context.prev = _context.next) {
          case 0:
            _context.next = 2;
            return fetchReddit(topic);

          case 2:
            json = _context.sent;

            console.log(json);

          case 4:
          case "end":
            return _context.stop();
        }
      }
    }, _callee, this);
  }));

  return function read(_x) {
    return _ref.apply(this, arguments);
  };
}();

function _asyncToGenerator(fn) { return function () { var gen = fn.apply(this, arguments); return new Promise(function (resolve, reject) { function step(key, arg) { try { var info = gen[key](arg); var value = info.value; } catch (error) { reject(error); return; } if (info.done) { resolve(value); } else { return Promise.resolve(value).then(function (value) { return step("next", value); }, function (err) { return step("throw", err); }); } } return step("next"); }); }; }

var fetch = require('isomorphic-fetch');

function fetchReddit(topic) {
  var redditUrl = "https://www.reddit.com/r/" + topic + ".json";
  return new Promise(function (resolve, reject) {
    fetch(redditUrl).then(function (response) {
      return response.json();
    }).then(function (result) {
      return resolve(result.data.children);
    });
  });
}

read('home');

software	version
Babel	6.5.2
node	4.3.0
npm	3.7.2
Operating System	OS X EL Capitan

[loganfsmyth]

The issue here is that you're using a function declaration, which because of hoisting is technically supposed to be at the top of the file. Babel doesn't know anything about require statements, so it has no way of knowing it is moving that logic above the code that it depends on.

Two options

1. Make a separate entry point, e.g.

   require("babel-core/register")
   require("babel-polyfill")
   
   require('./app') // load the app explicitly after the polyfill
   

2. Pass them when you start node, e.g.

   node -r babel-polyfill -r babel-core/register app.js

[devarsh]

@loganfsmyth thanks 👍