@babel/plugin-transform-async-to-generator

NOTE: This plugin is included in @babel/preset-env, in ES2017 In Babel 7, transform-async-to-module-method was merged into this plugin

Example

In

async function foo() {
  await bar();
}

Out

var _asyncToGenerator = function (fn) {
  ...
};
var foo = _asyncToGenerator(function* () {
  yield bar();
});

Out with options

Turn async functions into a Bluebird coroutine (caveats)

var Bluebird = require("bluebird");
var foo = Bluebird.coroutine(function*() {
  yield bar();
});

Installation

npm install --save-dev @babel/plugin-transform-async-to-generator

Usage

With a configuration file (Recommended)

Without options:

{
  "plugins": ["@babel/plugin-transform-async-to-generator"]
}

With options:

{
  "plugins": [
    [
      "@babel/plugin-transform-async-to-generator",
      {
        "module": "bluebird",
        "method": "coroutine"
      }
    ]
  ]
}

Via CLI

babel --plugins @babel/plugin-transform-async-to-generator script.js

Via Node API

require("@babel/core").transformSync("code", {
  plugins: ["@babel/plugin-transform-async-to-generator"],
});

Caveats

Bluebird non-promise runtime error

When using await with non-promise values, Bluebird will throw “Error: A value was yielded that could not be treated as a promise”. Since Babel cannot automatically handle this runtime error, you should manually transform it to a promise.

async function foo() {
-  await 42;
+  await Promise.resolve(42);
}

References

• Proposal: Async Functions for ECMAScript