regeneratorRuntime before v7.18.0

[Lancernix]

Hello, I have a strange problem about regenerator-runtime. I read the release document and found that after v7.18.0, when @babel/preset-env set useBuiltIns: 'entry', there is no need to import regenerator-runtime in the entry file. And before v7.18.0, if the regenerator-runtime is not imported, a “the regeneratorRuntime is not defined” error will appear. I verified this change on Babel's playground and my machine.
In the playground, the compiled result was as expected：

But on my machine, I did not import regenerator-runtime in the entry file, but there was a _ regeneratorRuntime function. This code can be executed successfully.

Why? I'm a little confused...

My env:

• MacBook Pro m1
• MacOS 13.2
• node v16.14.0

Demo git: https://github.com/Lancernix/babel-regenerator-demo

[nicolo-ribaudo]

regeneratorRuntime is now a "normal Babel helper". It's behavior is similar to, for example, the classCallCheck helper that Babel injects when compiling class A {}:

function _createClass(Constructor, protoProps, staticProps) { /* ... */ }
function _classCallCheck(instance, Constructor) { /* ... */ }
var A = /*#__PURE__*/_createClass(function A() {
  _classCallCheck(this, A);
});

By default, Babel injects all the helpers inline to make sure that they are available.

EDIT: hiding this part of the answer because I misread your question, it's a bit off topic

If you have multiple files and you want to avoid having the same helpers duplicated in every single file where they are used, you can use @babel/plugin-transform-runtime:

1. Install @babel/runtime in your dependencies, which is a package that contains all the runtime Babel helpers
2. Install @babel/plugin-transform-runtime to your dev dependencies (which is where you should usualy install all the @babel/* packages, since you only need them at dev time — except for @babel/runtime)
3. Add this plugin to your Babel config:

   "plugins": [
     ["@babel/plugin-transform-runtime", { "version": "7.21.0" }]
   ]

   where instead of 7.21.0 you write the version you installed of the @babel/runtime package.

The reason you are seeing the new behavior even with the old @babel/core and @babel/preset-env set to 7.17 is that the automatic injection of @babel/runtime has been implemented in @babel/plugin-transform-regenerator 7.18.0: if you check in your package-lock.json file, you have a modern version of that package.

[Lancernix]

Thanks! I checkedpackage-lock.json and found that the version of @babel/plugin-transform-regenerator is v7.20.5. I manually locked the version to v7.17.9 and got the same compiled result as Babel playground. So actually, v7.18.0 means the version of @babel/plugin-transform-regenerator!