babel 6 async / await: Unexpected token

Question

Im having trouble getting async / await transforms working. What am I missing?

My .babelrc:

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

My package.json (snipped):

{  
  "babel-core": "^6.1.2",
  "babel-plugin-transform-runtime": "^6.1.2",
  "babel-preset-es2015": "^6.1.2",
  "babel-preset-stage-0": "^6.1.2"
}

Output:

babel src/server
SyntaxError: src/server/index.js: Unexpected token (7:21)
   5 |
   6 | try {
>  7 |   let server = await server('localhost', env.NODE_PORT || 3000)
     |                      ^
   8 |   console.log(`Server started on ${server.info.uri}`)
   9 | } catch (err) {
  10 |   console.error('Error starting server: ', err)

Answer 1

According to this post you need to have babel-polyfill

Babel 6 regeneratorRuntime is not defined with async/await

Hopefully it'll help you :)

EDIT:

It doesn't have to be babel-polyfill but it's the only one I used.

As Gothdo said: the await keyword has to be in a function scope. Moreover, this function definition has to have the async keyword.

This means that you can not have the await keyword on the top-level scope.

Answer 2

Looks like async/await is only available in babel-preset-stage-3

http://babeljs.io/docs/plugins/preset-stage-3/

Answer 3

You can compile them yourself using the transform-async-to-module-method plugin, this allows you to compile them down to bluebird co-routines which requires ES6 generators (available in node4).

Or if you need to compile it back to ES5 so it's compatible for browsers you can use transform-async-to-generator and facebook's regenerator .

I've written about how to set up your babel config here http://madole.xyz/async-await-es7/

Answer 4

Use the Async to generator transform .

Installation

$ npm install babel-plugin-transform-async-to-generator

Usage

Add the following line to your .babelrc file:

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

Answer 5

It's recommended to upgrade to Babel 7 and use babel-env as opposed to stages (see here: https://github.com/babel/babel-upgrade ).

There's a command you can use to upgrade accordingly:

npx babel-upgrade