Are transform-runtime and regenerator-runtime meant to be used together?

[JoshRobertson]

Consider a babel config

      presets: [
        [
          "@babel/preset-env",
          {
            useBuiltIns: "entry",
            corejs: { version: "3.9", proposals: true },
            shippedProposals: true,
          },
        ],
        ["@babel/preset-react", { runtime: "automatic" }],
        "@babel/typescript"
      ],

      plugins: ["@babel/transform-runtime"]

relevant package.json

    "@babel/core": "^7.13.10",
    "@babel/plugin-transform-runtime": "^7.13.10",
    "@babel/preset-env": "^7.13.10",
    "@babel/preset-react": "^7.12.13",
    "@babel/preset-typescript": "^7.13.0",
    "@babel/runtime": "^7.13.10",
     "regenerator-runtime": "^0.13.7",

and a top-level polyfill file

import "core-js";
import "regenerator-runtime/runtime";

is this the right approach for useBuiltIns: entry and @babel/transform-runtime?

[nicolo-ribaudo]

Using both doesn't cause problems, but it's not necessary.

If you use @babel/plugin-transform-runtime, you can remove the regenerator-runtime/runtime import since it will be automatically loaded from @babel/runtime when needed.

[sag1v]

@nicolo-ribaudo Thanks for this answer.
Not sure if relevant here or deserves a new question, but what about core-js as a dependency? If using @babel/plugin-transform-runtime (with the corejs:3 option set) do you need to have core-js installed as dependency or does it baked-in already?

[nyngwang]

To @sag1v:

Hi, I can help you.

If using @babel/plugin-transform-runtime (with the corejs:3 option set) do you need to have core-js installed as dependency or does it baked-in already?

No, but you do need to install @babel/runtime-corejs3 instead of @babel/runtime, as instructed by the docs. By @babel/runtime-corejs3, it uses the special pure corejs behind the scene(and regenerator-runtime is on the next line btw). For reference, see #13698, which links to my StackOverflow Q&A, if you need an example.

I also recommend you read my comment there if you're new to Babel and have many confusions with it.