Babel 6 regeneratorRuntime is not defined

Question

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?

Answer 1

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"

Answer 2

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

Answer 3

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.

Answer 4

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", {
      "polyfill": false,
      "regenerator": true
    }]
  ]
}

Answer 5

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')],

Answer 6

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.