Using async/await in Node 6 with Babel

问题:

I'm trying to configure Babel for Node v6.9.2. I want to use async/await constructs.

Because I'm new to Babel and all Node infrastructure, I confused how to configure it properly:

• What preset should I use? Node is already implemented most of the ES6 features. So I don't want Babel to transpile features already supported by Node 6.9.x (arrow functions, new import mechanism etc) for performance reasons.

• What plugins should I include so I can use async/await? There I also confused, because after some researching I found several plugins: syntax-async-functions, transform-async-to-generator and some more.

Example of .babelrc will help.

Thanks

回答1:

What preset should I use?

You don't need to use any preset. Presets are just a collection of plugins which makes it easier to use if you want to transpile a set of features (for instance all ES2015 with preset-es2015). But when you want to transpile only a selection of these features, you only include the corresponding plugins.

What plugins should I include so I can use async/await?

Because Node 6 supports generators, you can use transform-async-to-generator with the following .babelrc:

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

And of course you would need to add plugins if you need to transpile more unsupported features.

Alternative babel-preset-env

babel-preset-env automatically determines what plugins you need for the specified environment. This will not include any plugins that are not necessary. To specify your current Node version you would use this .babelrc:

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

回答2:

Short answer

Use Babel preset for Node 6.x:

• https://www.npmjs.com/package/babel-preset-node6

Long answer

To see what ES feature is supported in a given Node version, see:

• http://node.green/

For async/await support in particular, see:

• http://node.green/#ES2017-features-async-functions

If you use Node v7.x (the current version) then you can use the --harmony flag and use async/await natively without transpilation.

Node v8.x (available as nightly builds) doesn't even need the --harmony flag for that.

But note that Node doesn't support import/export - to know why see:

• javascript - Why is there a spec for sync and async modules?
• Exporting Node module from promise result