Asked  6 Months ago    Answers:  5   Viewed   31 times

I'm trying to use async, await from scratch on Babel 6, but I'm getting regeneratorRuntime is not defined.

.babelrc file

    "presets": [ "es2015", "stage-0" ]

package.json file

"devDependencies": {
    "babel-core": "^6.0.20",
    "babel-preset-es2015": "^6.0.15",
    "babel-preset-stage-0": "^6.0.15"

.js file

"use strict";
async function foo() {
  await bar();
function bar() { }
exports.default = foo;

Using it normally without the async/await works just fine. Any ideas what I'm doing wrong?



babel-polyfill (deprecated as of Babel 7.4) is required. You must also install it in order to get async/await working.

npm i -D babel-core babel-polyfill babel-preset-es2015 babel-preset-stage-0 babel-loader


"devDependencies": {
  "babel-core": "^6.0.20",
  "babel-polyfill": "^6.0.16",
  "babel-preset-es2015": "^6.0.15",
  "babel-preset-stage-0": "^6.0.15"


  "presets": [ "es2015", "stage-0" ]

.js with async/await (sample code)

"use strict";

export default async function foo() {
  var s = await bar();

function bar() {
  return "bar";

In the startup file


If you are using webpack you need to put it as the first value of your entry array in your webpack configuration file (usually webpack.config.js), as per @Cemen comment:

module.exports = {
  entry: ['babel-polyfill', './test.js'],

  output: {
    filename: 'bundle.js'       

  module: {
    loaders: [
      { test: /.jsx?$/, loader: 'babel', }

If you want to run tests with babel then use:

mocha --compilers js:babel-core/register --require babel-polyfill
Tuesday, June 1, 2021
answered 6 Months ago

You need to manually create a symlink /usr/bin/node. Shortcut for bash compatible shells:

sudo ln -s `which nodejs` /usr/bin/node

Or if you use non-standard shells, just hardcode the path you find with which nodejs:

sudo ln -s /usr/bin/nodejs /usr/bin/node

Later edit

I found this explanation in the link you posted

There is a naming conflict with the node package (Amateur Packet Radio Node Program), and the nodejs binary has been renamed from node to nodejs. You'll need to symlink /usr/bin/node to /usr/bin/nodejs or you could uninstall the Amateur Packet Radio Node Program to avoid that conflict.

Later later edit

It's been a while since I answered this. Although the solution I posted up here worked for me several times, users have reported a few more solutions within the comments:

From @user229115

sudo update-alternatives --install /usr/bin/node node /usr/bin/nodejs 10

From AskUbuntu (user leftium)

sudo apt-get --purge remove node
sudo apt-get --purge remove nodejs
sudo apt-get install nodejs
Tuesday, June 1, 2021
answered 6 Months ago

I used import "babel-polyfill" and it solved my problem.

Update 2020: This answer is outdated, babel-polyfill is deprecated. Look into the docs and the answer by Jero.

Sunday, August 1, 2021
answered 4 Months ago

While I'm taking a different approach** to using Karma with Babel in my project, I suspect you're having the same problem I was: the Babel polyfill is not being loaded, and so you're not getting the functionality it supports (including the custom regenerator runtime that Babel uses to make generators work).

One approach would be to find a way to include the polyfill, perhaps by feeding it to Karma via the files array:

files: [
  'path/to/browser-polyfill.js', // edited: polyfill => browser-polyfill per P.Brian.Mackey's answer

An alternate approach may be to use Babel's runtime transformer [edit: on rereading the docs, this will not work unless you then browserify/webpack/etc. to process the require() calls created by the transformer]; per its docs,

The runtime optional transformer does three things:

  • Automatically requires babel-runtime/regenerator when you use generators/async functions.
  • Automatically requires babel-runtime/core-js and maps ES6 static methods and built-ins.
  • Removes the inline babel helpers and uses the module babel-runtime/helpers instead.

I have no experience with this, but I suspect you would do so by including the optional: ['runtime'] option from the Babel docs in your babelPreprocessor config, viz.:

'babelPreprocessor': {
  options: {
    optional: ['runtime'],  // per
    sourceMap: 'inline'

(** I'm currently using jspm + jspm-karma + some config to get the Babel polyfill to load in SystemJS; ask if relevant and I'll expound.)

Monday, August 2, 2021
answered 4 Months ago

You're not storing the connections on the server side. You're just setting them up on the server to communicate directly back and forth to the server. If you want messages going to the server to be sent back out to everyone, you need to set up the .on('message', ...) function for each connection on the server to have that behavior. To do this, you'll need to store the connections as they are created. Try this:

var WebSocketServer = require('websocket').server;
var http = require('http');

var server = http.createServer(function(request, response) {
    console.log((new Date()) + ' Received request for ' + request.url);
server.listen(5050, function() {
    console.log((new Date()) + ' Server is listening on port 5050');

wsServer = new WebSocketServer({
    httpServer: server,
    // You should not use autoAcceptConnections for production 
    // applications, as it defeats all standard cross-origin protection 
    // facilities built into the protocol and the browser.  You should 
    // *always* verify the connection's origin and decide whether or not 
    // to accept it. 
    autoAcceptConnections: false

function originIsAllowed(origin) {
  // put logic here to detect whether the specified origin is allowed. 
  return true;

//create an array to hold your connections
var connections = [];

wsServer.on('request', function(request) {
    if (!originIsAllowed(request.origin)) {
      // Make sure we only accept requests from an allowed origin 
      console.log((new Date()) + ' Connection from origin ' + request.origin + ' rejected.');
    var connection = request.accept('echo-protocol', request.origin);

    //store the new connection in your array of connections
    console.log((new Date()) + ' Connection accepted.');
    connection.on('message', function(message) {
        if (message.type === 'utf8') {
            console.log('Received Message: ' + message.utf8Data);

            //send the received message to all of the 
            //connections in the connection array
            for(var i = 0; i < connections.length; i++) {
        else if (message.type === 'binary') {
            console.log('Received Binary Message of ' + message.binaryData.length + ' bytes');
    connection.on('close', function(reasonCode, description) {
        console.log((new Date()) + ' Peer ' + connection.remoteAddress + ' disconnected.');
Monday, October 25, 2021
answered 1 Month ago
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