Do we need both of core-js and core-js-pure in the bundle?

[intelcoder]

I am using core-js to support IE11 mainly for promise and generator(Saga)
In my bundle I see core-js and core-js-pure. Do we need both of them?

I have some setup on babelrc.

["@babel/preset-env", {
      "useBuiltIns": "usage",
      "corejs": 3,
      "targets": {
        "ie": "11"
      }
}]

["@babel/transform-runtime", {
      "corejs": 3
}],
index.js

I have this code on my root for clientside
import 'core-js/stable'
import 'regenerator-runtime/runtime'

[zloirock]

No. It's 3 different ways of core-js usage. You should use only one of them:

• core-js direct import
• core-js injecting by usage plugin from @babel/preset-env
• core-js injecting without global pollution by @babel/transform-runtime plugin

[perqa]

What if I include a library which uses core-js-pure into my app which only uses core-js by direct import? I guess it is inevitable then to get both core-js-pure and core-js in the bundle?

[zloirock]

@perqa yes. Now, since core-js and core-js-pure have the same commonjs API structure, you can try to configure webpack aliases or something similar, but it can be dangerous. However, I'm planning to add a way to avoid this duplication properly. This issue is tracked in #833.