Is babel-polyfill more than just a polyfill?

The docs for https://babeljs.io/docs/usage/polyfill/ are confusing:

Babel includes a polyfill that includes a custom regenerator runtime and core.js.

Since core.js is a polyfill for the missing methods (String.prototype.includes() etc), what does the ‘custom regenerator’ add?

If the ‘custom regenerator’ does code transformation like babel, wouldn’t everybody already be shipping ES5 code that’s been transformed by babel?

In short: if I just need a polyfill, and nothing else (since I’m already using babel during my build process), should I be using babel-polyfill or core.js? The current docs do nit make it clear.

[mikemaccana]

Thanks @thejameskyle . My previous impression was that the ES5 code was more plain, I now get what the babel runtime does.

Since most people who use Babel haven’t written a compiler before (and since ‘runtime’ is sometimes used as a synonym for VM) it could also be worth making ‘babel runtime’ a link explaining the same thing your comment does.

[mikemaccana]

@thejameskyle assuming what @zloirock said is correct (and my own understanding is correct):

Polyfills

If you’re already transforming to ES6 during your build process

If you’re already using babel to transform your code during your build process, you can load the core-js polyfill to add the additional methods provided by ES6 and ES7. (Add details here)

require("core-js"); 

If you wish to transform ES5 to ES6 in the browser

If you are not using babel to transform your code as part of your build steps, and want to ship ES^ to the browser, you can use get both the systax transformations and the additional methods with:

require("babel-polyfill");