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 entry 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

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.

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
    }]
  ]
}

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

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.

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-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
]