Develop Reference

ReferenceError: regeneratorRuntime is not defined working on vanilla js [duplicate]

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
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

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

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.

Update: The Babel 7 post also has a more in-depth answer.
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
This alternative has no global scope pollution and is suitable for libraries.
{
"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 corejs polyfill is used, you replace #babel/runtime with #babel/runtime-corejs2 (for "corejs": 2) or #babel/runtime-corejs3 (for "corejs": 3).

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"
]
}

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'],
};

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
]

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"
}
}
]
]
}

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

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.

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 had this problem in Chrome. Similar to RienNeVaPlu͢s’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 used tip from https://github.com/babel/babel/issues/9849#issuecomment-592668815 and added targets: { esmodules: true,} to my babel.config.js.
module.exports = {
presets: [
[
'#babel/preset-env',
{
targets: {
esmodules: true,
},
},
],
],
}

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 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:
As mentioned above many times, I needed to add babel-polyfill into my webpack entry array:
...
entry: ['babel-polyfill', './index.js'],
...
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.

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"

There are so many answers up there, I will post my answer for my reference.
I use webpack and react, here is my solution without the .babelrc file
I am working on this in Aug 2020
Install react and babel
npm i #babel/core babel-loader #babel/preset-env #babel/preset-react react react-dom #babel/plugin-transform-runtime --save-dev
Then in my webpack.config.js
// other stuff
module.exports = {
// other stuff
module: {
rules: [
{
test: /\.m?js$/,
exclude: /(node_modules|bower_components)/,
use: {
loader: 'babel-loader',
options: {
presets: ['#babel/preset-env',"#babel/preset-react"],
plugins: ['#babel/plugin-proposal-class-properties', '#babel/plugin-transform-runtime'],
//npm install --save-dev #babel/plugin-transform-runtime
}
}
},
],
},
};
I just don't know why I dont need to install the async package for the moment

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
}]
]
}

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";
....

Easiest way to fix this 'regeneratorRuntime not defined issue' in your console:
You don't have to install any unnecessary plugins. Just add:
<script src="https://unpkg.com/regenerator-runtime#0.13.1/runtime.js"></script>
inside of the body in your index.html.
Now regeneratorRuntime should be defined once you run babel and now your async/await functions should be compiled successfully into ES2015

Just install regenerator-runtime
with below command
npm i regenerator-runtime
add below line in startup file before you require server file
require("regenerator-runtime/runtime");
So far this has been working for me

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>

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/

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')],

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

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 use mocha with the --require babel-polyfill option:
mocha --require babel-polyfill

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'));
...

Not able to build node js project for a specifc imported library

I am importing libraries in my vue.js project. For Library1 alone there are no errors. When i run my vue node js project build for library 2 i am importing , it always fails at below line and gets stuck with message 'building for production'.
Could not find implementations for the following rules specified in the configuration:
no-explicit-any
Try upgrading TSLint and/or ensuring that you have all necessary custom rules installed.
If TSLint was recently upgraded, you may have old rules configured which need to be cleaned up.
Is there a way to make this ignore by npm build ?
Below is my .eslintrc.js
module.exports = {
root: true,
env: {
node: true
},
'extends': [
'plugin:vue/essential',
'eslint:recommended',
'#vue/typescript/recommended'
],
parserOptions: {
ecmaVersion: 2020,
ecmaFeatures: {
legacyDecorators: true,
},
},
rules: {
'#typescript-eslint/no-var-requires': 0,
'#typescript-eslint/ban-ts-ignore': 'off',
"#typescript-eslint/no-explicit-any": "off",
}
}
Do i need to update my tsconfig or tslint to stop checking for this when building production. This happens to only my vue library projecting i am using.
I use npm link and npm link to link and install libraries.

Well the easiest way to fix it is by removing tslint. As you Already have eslint. You just have have to install some extra eslint packages
npm i -D #typescript-eslint/eslint-plugin;
npm i -D #typescript-eslint/parser;
npm i -D eslint;
The following is the recommended
module.exports = {
env: {
commonjs: true,
es6: true,
node: true,
},
extends: [
"eslint:recommended",
"plugin:#typescript-eslint/eslint-recommended",
"plugin:#typescript-eslint/recommended",
"plugin:#typescript-eslint/recommended-requiring-type-checking",
],
globals: {
Atomics: "readonly",
SharedArrayBuffer: "readonly",
},
parser: "#typescript-eslint/parser",
parserOptions: {
project: "./tsconfig.json",
ecmaVersion: 2019,
},
plugins: ["#typescript-eslint"],
rules: {
.....
}
}
NOTE:
on your tsconfig.json
Add the include section. This as the name says includes the paths of your source files. And exclude does the opposite
{
"compilerOptions": {
....
},
"exclude": [
"/node_modules/",
"./config/"
],
"include": [
"./src/*.ts",
"./src/**/*.ts",
"./src/**/**/*.ts",
"./src/**/**/**/*.ts"
]
}

Eslint does not allow static class properties

I'm current developing an API on Node 12.14.1 and using Eslint to help me write the code.
Unfortunately it does not allow me to set static class properties as shown below:
class AuthManager {
static PROP = 'value'
}
The following error is given: Parsing error: Unexpected token =eslint
Static class properties are already supported on JS and on Node.
How can this rule be disable?
I also have the following .eslintrc.json file:
{
"env": {
"es6": true,
"node": true
},
"extends": "eslint:recommended",
"globals": {
"Atomics": "readonly",
"SharedArrayBuffer": "readonly"
},
"parserOptions": {
"ecmaVersion": 2018,
"sourceType": "module"
}
}

ESLint v8 now supports static class properties natively: https://eslint.org/blog/2021/10/eslint-v8.0.0-released
parserOptions ecmaVersion should be set to 13, 2022, or "latest" to enable the support.
Add this to your .eslint.(cjs | json | js)
{
parserOptions: {
ecmaVersion: 2022,
}
}

ESLint with its default parser does not support class fields syntax for now. You can solve the problem by changing the configured parser to babel-eslint.
npm install --save-dev babel-eslint
// eslintrc.json
{
"parser": "babel-eslint",
...
}
Eslint's default parser, Espree, does not support class fields because that syntax is currently stage 3, and that it is decided that only stage 4 proposals are to be supported in Espree.

As of now, I had to use these configs
.eslintrc.js
module.exports = {
env: {
node: true,
es6: true,
},
extends: [
'airbnb-base',
],
parser: '#babel/eslint-parser',
parserOptions: {
babelOptions: {
configFile: './.babelrc',
},
ecmaVersion: 2018, // needed to support spread in objects
},
plugins: ['#babel'],
};
.babelrc
{
"presets": ["#babel/env"],
"plugins": [
"#babel/plugin-syntax-class-properties"
]
}
For which I had to install:
npm i -D #babel/preset-env
npm i -D #babel/eslint-parser
npm i -D #babel/eslint-plugin
npm i -D #babel/plugin-syntax-class-properties
Notice that the #babel modules above are the only #babel modules in my package.json.

you need to install #babel/eslint-parser:
yarn add --dev #babel/eslint-parser
And have the parser in your .eslintrc.yml for instance:
parser: "#babel/eslint-parser"

Set version of EcmaScript generated by Babel, in react app

I'm using the latest ES8 features in my react code, for example, async and await. Because of misconfiguration problem in my webpack config, I cannot use source maps, and this slows down debugging.
A quick solution could be to locally compile source code into ES7 or ES8, and test in the latest Chrome. How can I set this in .babelrc? Here's my current .babelrc:
{
"presets": [
"react-app"
]
}

Answered here,
{
"presets": [
"react",
["env", {
"targets": {
"chrome": 67
}
}]
]
}
As of Jul 2018, the above setting would not support spread operator in objects. To enable it,
npm install --save-dev babel-plugin-transform-object-rest-spread
Use the following configuration in .babelrc:
{
"presets": [
"react",
["env", {
"targets": {
"chrome": 67
}
}]
],
"plugins": ["transform-object-rest-spread"]
}

How to configure StandardJS?

One of the main features of StandardJS is that it doesn't require configuration.
The problem is that I want to configure it. I don't want to put:
/* eslint-env mocha */
...in every test file. I want to configure StandardJS to treat everything in the test directory as mocha tests.
I've found in the README that some configuration is possible, e.g.:
{
"standard": {
"globals": [ "myVar1", "myVar2" ]
}
}
...but I'm struggling to find more comprehensive documentation about the configuration options. Is it possible to configure StandardJS to treat files in different directories differently?

You have a couple of options to try out and see what works for your specific project depending on the recent implementation of StandardJS.
Define your own globals
in package.json:
"standard": {
"globals": [
"describe",
"before",
"after",
"beforeEach",
"afterEach",
"it",
"assert"
]
}
or in .eslintrc:
{
"globals": {
"describe": false,
"before": false,
"after": false,
"beforeEach": false,
"afterEach": false,
"it": false,
"assert": false
}
}
More on ESLint's configuration.
Define an environment
in package.json:
"standard": {
"env": {
"mocha": true
}
}
or in .eslintrc:
{
"env": {
"mocha": true
}
}
Check out currently available environments
Run StandardJS as an NPM script with the environment specified
in package.json:
{
"scripts": {
"lint": "standard --env mocha"
}
}
Use a plugin
after installing the plugin (e.g. eslint-plugin-mocha)
in package.json:
"standard": {
"plugins": [
"mocha"
]
}
or in .eslintrc:
{
"plugins": [
"mocha"
]
}
Create your own, customized rules based on StandardJS
Check out this repository. The quick rundown:
Install with:
npm install --save-dev eslint-config-standard eslint-plugin-standard eslint-plugin-promise eslint-plugin-import eslint-plugin-node
Then create a .eslintrc file by extending StandardJS and start to fill with your own rules:
{
"extends": "standard"
}
Since StandardJS uses ESLint under the hood, you can pretty much configure it however you want it using ESLint's documentation.