使用 Babel.js 转译 Async Await 提案? [英] Transpile Async Await proposal with Babel.js?

问题描述

有一个引入 C# 风格 async-await 的提议.我知道 Babel.js 可以将 ES6 转换为 ES5，但是有没有办法让它将 async-await 转换为 ES5?

There is a proposal for introducing C# style async-await. I know Babel.js transpiles ES6 to ES5, but is there any way to make it transpile async-await to ES5?

推荐答案

Babel v6

从 Babel v6 开始，Babel 本身不再包含任何转换器.您必须明确指定要转换的任何功能.

实现此功能的最快方法是使用 presets，其中已经包含转换 ES2015 和更新提案所需的插件集.对于 async，您将需要 es2015 和 es2017 预设和 runtime 插件(不要忘记安装 babel-runtime 如文档中所述):

The quickest way to get this working is to use presets which already contain the set of plugins needed to transform ES2015 and newer proposals. For async, you will need the es2015 and es2017 presets and the runtime plugin (don't forget to install babel-runtime as described in the documentation):

{
  "presets": [
    "es2015",
    "es2017"
  ],
  "plugins": [
    "transform-runtime"
  ]
}

预设 - ES2015 环境

如果您在支持 ES2015(更具体地说，生成器和 Promises)的环境中运行代码，那么您只需要 es2017 预设:

Presets - ES2015 environment

If you run the code in an environment that supports ES2015 (more specifically, generators and Promises), then all you need is the es2017 preset:

{
  "presets": [
    "es2017"
  ]
}

自定义

要仅转换 async 功能，您将需要以下插件.

Custom

To only transform the async functions, you will need the following plugins.

syntax-async-functions 是在任何情况下都需要能够解析异步函数

syntax-async-functions is needed in any every case to be able to parse async functions

为了运行异步函数，你要么需要使用

In order to run the async function, you either need to use

• transform-async-to-generator:将 async 函数转换为生成器.这将使用 Babel 自己的协程"实现.
• transform-async-to-module-method:同样将 async 函数转换为生成器，但传递给配置中指定的模块和方法，而不是 Babel 自己的方法.这允许您使用外部库，例如 bluebird.

• transform-async-to-generator: Converts the async function into a generator. This will use Babel's own "co-routine" implementation.
• transform-async-to-module-method: Also converts the async function to a generator, but passes it to the module and method specified in the configuration instead of Babel's own method. This allows you to use external libraries such as bluebird.

如果您的代码在支持生成器的环境中运行，那么就没有什么可做的了.但是，如果目标环境不支持生成器，您还必须转换生成器.这是通过 transform-regenerator 转换完成的.这个转换依赖于运行时函数，所以你还需要 Babel 的 transform-runtime 转换(+ babel-runtime 包).

If your code runs in an environment that supports generators, then there is nothing left to do. However, if the target environment does not support generators, you will also have to transform the generator. This is done via the transform-regenerator transform. This transform depends on runtime functions, so you will also need Babel's transform-runtime transform (+ the babel-runtime package).

异步生成器

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

异步到模块方法

{
  "plugins": [
    "syntax-async-functions",
   ["transform-async-to-module-method", {
     "module": "bluebird",
     "method": "coroutine"
   }]
  ]
}

异步生成器 + 再生器

{
  "plugins": [
    "syntax-async-functions",
    "transform-async-to-generator",
    "transform-regenerator",
    "transform-runtime"
  ]
}

<小时>

Babel v4 及更早版本

是的，您必须启用实验转换器.Babel 使用 regenerator.

---

Babel v4 and older

Yes, you have to enable the experimental transformers. Babel uses regenerator.

使用

$ babel --experimental

<小时>

babel.transform("code", { experimental: true });

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