Babel 6 regeneratorRuntime is not defined


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 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

package.json

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

.babelrc

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

.js with async/await (sample code)

"use strict";

export default async function foo() {
  var s = await bar();
  console.log(s);
}

function bar() {
  return "bar";
}

In the startup file

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

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

Besides polyfill, I use babel-plugin-transform-runtime. The plugin is described as:

Externalize references to helpers and builtins, automatically polyfilling your code without polluting globals. What does this actually mean though? Basically, you can use built-ins such as Promise, Set, Symbol etc as well use all the Babel features that require a polyfill seamlessly, without global pollution, making it extremely suitable for libraries.

It also includes support for async/await along with other built-ins of ES 6.

$ npm install --save-dev babel-plugin-transform-runtime

In .babelrc, add the runtime plugin

{
  "plugins": [
    ["transform-runtime", {
      "regenerator": true
    }]
  ]
}

Note If you're using babel 7, the package has been renamed to @babel/plugin-transform-runtime.


Babel 7 Users

I had some trouble getting around this since most information was for prior babel versions. For Babel 7, install these two dependencies:

npm install --save @babel/runtime 
npm install --save-dev @babel/plugin-transform-runtime

And, in .babelrc, add:

{
    "presets": ["@babel/preset-env"],
    "plugins": [
        ["@babel/transform-runtime"]
    ]
}

Update

It works if you set the target to Chrome. But it might not work for other targets, please refer to: https://github.com/babel/babel-preset-env/issues/112

So this answer is NOT quite proper for the original question. I will keep it here as a reference to babel-preset-env.

A simple solution is to add import 'babel-polyfill' at the beginning of your code.

If you use webpack, a quick solution is to add babel-polyfill as shown below:

entry: {
    index: ['babel-polyfill', './index.js']
}

I believe I've found the latest best practice.

Check this project: https://github.com/babel/babel-preset-env

yarn add --dev babel-preset-env

Use the following as your babel configuration:

{
  "presets": [
    ["env", {
      "targets": {
        "browsers": ["last 2 Chrome versions"]
      }
    }]
  ]
}

Then your app should be good to go in the last 2 versions of Chrome browser.

You can also set Node as the targets or fine-tune the browsers list according to https://github.com/ai/browserslist

Tell me what, don't tell me how.

I really like babel-preset-env's philosophy: tell me which environment you want to support, do NOT tell me how to support them. It's the beauty of declarative programming.

I've tested async await and they DO work. I don't know how they work and I really don't want to know. I want to spend my time on my own code and my business logic instead. Thanks to babel-preset-env, it liberates me from the Babel configuration hell.


Alternatively, if you don't need all the modules babel-polyfill provides, you can just specify babel-regenerator-runtime in your webpack config:

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

  // ...
};

When using webpack-dev-server with HMR, doing this reduced the number of files it has to compile on every build by quite a lot. This module is installed as part of babel-polyfill so if you already have that you're fine, otherwise you can install it separately with npm i -D babel-regenerator-runtime.


My simple solution:

npm install --save-dev babel-plugin-transform-runtime
npm install --save-dev babel-plugin-transform-async-to-generator

.babelrc

{
  "presets": [
    ["latest", {
      "es2015": {
        "loose": true
      }
    }],
    "react",
    "stage-0"
  ],
  "plugins": [
    "transform-runtime",
    "transform-async-to-generator"
  ]
}

Babel 7.4.0 or later (core-js 2 / 3)

As of Babel 7.4.0, @babel/polyfill is deprecated.

In general, there are two ways to install polyfills/regenerator: via global namespace (Option 1) or as ponyfill (Option 2, without global pollution).


Option 1: @babel/preset-env

presets: [
  ["@babel/preset-env", {
    useBuiltIns: "usage",
    corejs: 3, // or 2,
    targets: {
        firefox: "64", // or whatever target to choose .    
    },
  }]
]

will automatically use regenerator-runtime and core-js according to your target. No need to import anything manually. Don't forget to install runtime dependencies:

npm i --save regenerator-runtime core-js

Alternatively, set useBuiltIns: "entry" and import it manually:

import "regenerator-runtime/runtime";
import "core-js/stable"; // if polyfills are also needed

Option 2: @babel/transform-runtime with @babel/runtime (no global scope pollution)

{
  "plugins": [
    [
      "@babel/plugin-transform-runtime",
      {
        "regenerator": true,
        corejs: 3 // or 2; if polyfills needed
        ...
      }
    ]
  ]
}

Install it:

npm i -D @babel/plugin-transform-runtime
npm i @babel/runtime

If you use core-js polyfills, you install @babel/runtime-corejs2 or @babel/runtime-corejs3 instead, see here.

Cheers


babel-regenerator-runtime is now deprecated, instead one should use regenerator-runtime.

To use the runtime generator with webpack and babel v7:

install regenerator-runtime:

npm i -D regenerator-runtime

And then add within webpack configuration :

entry: [
  'regenerator-runtime/runtime',
  YOUR_APP_ENTRY
]

Be careful of hoisted functions

I had both my 'polyfill import' and my 'async function' in the same file, however I was using the function syntax that hoists it above the polyfill which would give me the ReferenceError: regeneratorRuntime is not defined error.

Change this code

import "babel-polyfill"
async function myFunc(){ }

to this

import "babel-polyfill"
var myFunc = async function(){}

to prevent it being hoisted above the polyfill import.


Update your .babelrc file according to the following examples, it will work.

If you are using @babel/preset-env package

{
  "presets": [
    [
      "@babel/preset-env", {
        "targets": {
          "node": "current"
        }
      }
    ]
  ]
}
or if you are using babel-preset-env package

{
  "presets": [
    [
      "env", {
        "targets": {
          "node": "current"
        }
      }
    ]
  ]
}

If using babel-preset-stage-2 then just have to start the script with --require babel-polyfill.

In my case this error was thrown by Mocha tests.

Following fixed the issue

mocha \"server/tests/**/*.test.js\" --compilers js:babel-register --require babel-polyfill


I started getting this error after converting my project into a typescript project. From what I understand, the problem stems from async/await not being recognized.

For me the error was fixed by adding two things to my setup:

  1. As mentioned above many times, I needed to add babel-polyfill into my webpack entry array:

    ...
    
    entry: ['babel-polyfill', './index.js'],
    
    ...
  2. I needed to update my .babelrc to allow the complilation of async/await into generators:

    {
      "presets": ["es2015"],
      "plugins": ["transform-async-to-generator"]
    }

DevDependencies:

I had to install a few things into my devDependencies in my package.json file as well. Namely, I was missing the babel-plugin-transform-async-to-generator, babel-polyfill and the babel-preset-es2015:

 "devDependencies": {
    "babel-loader": "^6.2.2",
    "babel-plugin-transform-async-to-generator": "^6.5.0",
    "babel-polyfill": "^6.5.0",
    "babel-preset-es2015": "^6.5.0",
    "webpack": "^1.12.13"
 }

Full Code Gist:

I got the code from a really helpful and concise GitHub gist you can find here.


As of Oct 2019 this worked for me:

Add this to the preset.

 "presets": [
      "@babel/preset-env"
    ]

Then install regenerator-runtime using npm.

npm i regenerator-runtime

And then in your main file use: (this import is used only once)

import "regenerator-runtime/runtime";

This is will enable you to use async awaits in your file and remove the regenerator error


You're getting an error because async/await use generators, which are an ES2016 feature, not ES2015. One way to fix this is to install the babel preset for ES2016 (npm install --save babel-preset-es2016) and compile to ES2016 instead of ES2015:

"presets": [
  "es2016",
  // etc...
]

As the other answers mention, you can also use polyfills (though make sure you load the polyfill first before any other code runs). Alternatively, if you don't want to include all of the polyfill dependencies, you can use the babel-regenerator-runtime or the babel-plugin-transform-runtime.


I had this problem in Chrome. Similar to RienNeVaPlu?s’s answer, this solved it for me:

npm install --save-dev regenerator-runtime

Then in my code:

import 'regenerator-runtime/runtime';

Happy to avoid the extra 200 kB from babel-polyfill.


I fixed this error by installing babel-polyfill

npm install babel-polyfill --save

then I imported it in my app entry point

import http from 'http';
import config from 'dotenv';
import 'babel-polyfill';
import { register } from 'babel-core';
import app from '../app';

for testing I included --require babel-polyfill in my test script

"test": "export NODE_ENV=test|| SET NODE_ENV=test&& mocha --compilers 
  js:babel-core/register --require babel-polyfill server/test/**.js --exit"

New Answer Why you follow my answer ?

Ans: Because I am going to give you a answer with latest Update version npm project .

04/14/2017

"name": "es6",
 "version": "1.0.0",
   "babel-core": "^6.24.1",
    "babel-loader": "^6.4.1",
    "babel-polyfill": "^6.23.0",
    "babel-preset-es2015": "^6.24.1",
    "webpack": "^2.3.3",
    "webpack-dev-server": "^2.4.2"

If your Use this version or more UP version of Npm and all other ... SO just need to change :

webpack.config.js

module.exports = {
  entry: ["babel-polyfill", "./app/js"]
};

After change webpack.config.js files Just add this line to top of your code .

import "babel-polyfill";

Now check everything is ok. Reference LINK

Also Thanks @BrunoLM for his nice Answer.


The targeted browsers I need to support already support async/await, but when writing mocha tests, without the proper setting I still got this error.

Most of the articles I googled are outdated, including the accepted answer and high voted answers here, i.e. you don't need polyfill, babel-regenerator-runtime, babel-plugin-transform-runtime. etc. if your target browser(s) already supports async/await (of course if not you need polyfill)

I don't want to use webpack either.

Tyler Long's answer is actually on the right track since he suggested babel-preset-env (but I omitted it first as he mentioned polifill at the beginning). I still got the ReferenceError: regeneratorRuntime is not defined at the first then I realized it was because I didn't set the target. After setting the target for node I fix the regeneratorRuntime error?

  "scripts": {
    //"test": "mocha --compilers js:babel-core/register"
    //https://github.com/mochajs/mocha/wiki/compilers-deprecation
    "test": "mocha --require babel-core/register"
  },
  "devDependencies": {
    "babel-core": "^6.26.3",
    "babel-preset-env": "^1.7.0",
    "mocha": "^5.2.0"
  },
  //better to set it .bablerc, I list it here for brevity and it works too.
  "babel": {
    "presets": [
      ["env",{
        "targets": {
          "node": "current"
           "chrome": 66,
           "firefox": 60,
        },
        "debug":true
      }]
    ]
  }

To babel7 users and ParcelJS >= 1.10.0 users

npm i @babel/runtime-corejs2
npm i --save-dev @babel/plugin-transform-runtime @babel/core

.babelrc

{
  "plugins": [
    ["@babel/plugin-transform-runtime", {
      "corejs": 2
    }]
  ]
}

taken from https://github.com/parcel-bundler/parcel/issues/1762


1 - Install babel-plugin-transform-async-to-module-method, babel-polyfil, bluebird , babel-preset-es2015, babel-core :

npm install babel-plugin-transform-async-to-module-method babel-polyfill bluebird babel-preset-es2015 babel-core

2 - Add in your js babel polyfill:

import 'babel-polyfill';

3 - Add plugin in your .babelrc:

{
    "presets": ["es2015"],
    "plugins": [
      ["transform-async-to-module-method", {
        "module": "bluebird",
        "method": "coroutine"
      }]
    ]
}

Source : http://babeljs.io/docs/plugins/transform-async-to-module-method/


I had a setup
with webpack using presets: ['es2015', 'stage-0']
and mocha that was running tests compiled by webpack.

To make my async/await in tests work all I had to do is add mocha --require babel-polyfill option.


I get this error using gulp with rollup when I tried to use ES6 generators:

gulp.task('scripts', () => {
  return rollup({
    entry: './app/scripts/main.js',
    format: "iife",
    sourceMap: true,
    plugins: [babel({
      exclude: 'node_modules/**',
      "presets": [
        [
          "es2015-rollup"
        ]
      ],
      "plugins": [
        "external-helpers"
      ]
    }),
    includePaths({
      include: {},
      paths: ['./app/scripts'],
      external: [],
      extensions: ['.js']
    })]
  })

  .pipe(source('app.js'))
  .pipe(buffer())
  .pipe(sourcemaps.init({
    loadMaps: true
  }))
  .pipe(sourcemaps.write('.'))
  .pipe(gulp.dest('.tmp/scripts'))
  .pipe(reload({ stream: true }));
});

I may case the solution was to include babel-polyfill as bower component:

bower install babel-polyfill --save

and add it as dependency in index.html:

<script src="/bower_components/babel-polyfill/browser-polyfill.js"></script>

For people looking to use the babel-polyfill version 7^ do this with webpack ver3^.

Npm install the module npm i -D @babel/polyfill

Then in your webpack file in your entry point do this

entry: ['@babel/polyfill', path.resolve(APP_DIR, 'App.js')],

My working babel 7 boilerplate for react with regenerator runtime:

.babelrc

{
  "presets": [
    [
      "@babel/preset-env",
      {
        "targets": {
          "node": true,
        },
      },
    ],
    "@babel/preset-react",
  ],
  "plugins": [
    "@babel/plugin-syntax-class-properties",
    "@babel/plugin-proposal-class-properties"
  ]
}

package.json

...

"devDependencies": {
  "@babel/core": "^7.0.0-0",
  "@babel/plugin-proposal-class-properties": "^7.4.4",
  "@babel/plugin-syntax-class-properties": "^7.2.0",
  "@babel/polyfill": "^7.4.4",
  "@babel/preset-env": "^7.4.5",
  "@babel/preset-react": "^7.0.0",
  "babel-eslint": "^10.0.1",
...

main.js

import "@babel/polyfill";

....

If you are building an app, you just need the @babel/preset-env and @babel/polyfill:

npm i -D @babel/preset-env
npm i @babel/polyfill

(Note: you don't need to install the core-js and regenerator-runtime packages because they both will have been installed by the @babel/polyfill)

Then in .babelrc:

{
  "presets": [
    [
      "@babel/preset-env",
      {
        "useBuiltIns": "entry"  // this is the key. use 'usage' for further codesize reduction, but it's still 'experimental'
      }
    ]
  ]
}

Now set your target environments. Here, we do it in the .browserslistrc file:

# Browsers that we support

>0.2%
not dead
not ie <= 11
not op_mini all

Finally, if you went with useBuiltIns: "entry", put import @babel/polyfill at the top of your entry file. Otherwise, you are done.

Using this method will selectively import those polyfills and the 'regenerator-runtime' file(fixing your regeneratorRuntime is not defined issue here) ONLY if they are needed by any of your target environments/browsers.


for future reference :

As of Babel version 7.0.0-beta.55 stage presets have been removed

refer blog https://babeljs.io/blog/2018/07/27/removing-babels-stage-presets

async await can be still be used by

https://babeljs.io/docs/en/babel-plugin-transform-async-to-generator#usage

installation

npm install --save-dev @babel/plugin-transform-async-to-generator

usage in .babelrc

 { 
     "presets": ["@babel/preset-env"],
     "plugins": ["@babel/plugin-transform-async-to-generator"]
 }

and using babel polyfill https://babeljs.io/docs/en/babel-polyfill

installation

npm install --save @babel/polyfill

webpack.config.js

module.exports = {
  entry: ["@babel/polyfill", "./app/js"],
};

If you using Gulp + Babel for a frontend you need to use babel-polyfill

npm install babel-polyfill

and then add a script tag to index.html above all other script tags and reference babel-polyfill from node_modules


Most of these answers recommend solutions for dealing with this error using WebPack. But in case anyone is using RollUp (like I am), here is what finally worked for me (just a heads-up and bundling this polyfill ads about 10k tot he output size):

.babelrc

{
    "presets": [
        [
            "env",
            {
                "modules": false,
                "targets": {
                    "browsers": ["last 2 versions"]
                }
            }
        ]
    ],
    "plugins": ["external-helpers",
        [
            "transform-runtime",
            {
                "polyfill": false,
                "regenerator": true
            }
        ]]
}

rollup.config.js

import resolve from 'rollup-plugin-node-resolve';
import babel from 'rollup-plugin-babel';
import uglify from 'rollup-plugin-uglify';
import commonjs from 'rollup-plugin-commonjs';


export default {
    input: 'src/entry.js',
    output: {
        file: 'dist/bundle.js',
        format: 'umd',
        name: 'MyCoolLib',
        exports: 'named'
    },
    sourcemap: true,
    plugins: [
        commonjs({
            // polyfill async/await
            'node_modules/babel-runtime/helpers/asyncToGenerator.js': ['default']
        }),
        resolve(),
        babel({
            runtimeHelpers: true,
            exclude: 'node_modules/**', // only transpile our source code
        }),
        uglify()

    ]
};

I am using a React and Django project and got it to work by using regenerator-runtime. You should do this because @babel/polyfill will increase your app's size more and is also deprecated. I also followed this tutorial's episode 1 & 2 to create my project's structure.

*package.json*

...
"devDependencies": {
    "regenerator-runtime": "^0.13.3",
    ...
}

.babelrc

{
   "presets": ["@babel/preset-env", "@babel/preset-react"],
   "plugins": ["transform-class-properties"]
}

index.js

...
import regeneratorRuntime from "regenerator-runtime";
import "regenerator-runtime/runtime";
ReactDOM.render(<App />, document.getElementById('app'));
...

This solution is out of date.

I found the solution in the youtube comments of this video https://www.youtube.com/watch?v=iWUR04B42Hc&lc=Ugyq8UJq-OyOzsKIIrB4AaABAg

This should direct to the correct comment. Much props to "beth w" for finding the solution.

Beth W 3 months ago (edited)
Another change I had to make in 2019 - babel no longer uses the stage-0 preset as of v7 apparently, so at 26:15 instead of 'npm install --save-dev babel-polyfill babel-preset-stage-0', I had to do:

npm install --save @babel/polyfill

Which covers both of the older options. Then, in the entry point for the app I > included '@babel/polyfill', and in the query presets I left it as-is. So the webpack config ends up looking like:

const path = require('path');
module.exports = {
    entry: {
        app: ['@babel/polyfill', './src/app.js']
    },
    output: {
        path: path.resolve(__dirname, 'build'),
        filename: 'app.bundle.js'
    },
    mode: 'development',
    module: {
        rules: [{
            test: /\.js?$/,
            exclude: /node_modules/,
            loader: 'babel-loader',
            query: {
                presets: ['@babel/preset-env']
            }
        }]
    }
}

Hope that helps someone!


This error is caused when async/await functions are used without the proper Babel plugins. As of March 2020, the following should be all you need to do. (@babel/polyfill and a lot of the accepted solutions have been deprecated in Babel. Read more in the Babel docs.)

In the command line, type:

npm install --save-dev @babel/plugin-transform-runtime

In your babel.config.js file, add this plugin @babel/plugin-transform-runtime. Note: The below example includes the other presets and plugins I have for a small React/Node/Express project I worked on recently:

module.exports = {
  presets: ['@babel/preset-react', '@babel/preset-env'],
  plugins: ['@babel/plugin-proposal-class-properties', 
  '@babel/plugin-transform-runtime'],
};

In 2019 with Babel 7.4.0+, babel-polyfill package has been deprecated in favor of directly including core-js/stable ([email protected]+, to polyfill ECMAScript features) and regenerator-runtime/runtime (needed to use transpiled generator functions):

import "core-js/stable";
import "regenerator-runtime/runtime";

Information from babel-polyfill documentation.