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Address duplicate core-js import #9097

lerayne opened this Issue Nov 29, 2018 · 2 comments


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lerayne commented Nov 29, 2018

Feature Request

This is related to @babel/preset-env and @babel/runtime

useBuiltIns:usage is a great feature that helps avoiding unnecessary polyfills. The drawback though is that other libraries still import core-js explicitly. Because of that, I usually have many core-js modules imported twice:


Once as /core-js/modules (via @babel/runtime with 'useBuiltIns:usage') and the second time as /core-js/library/modules

I assume there should be the way to avoid that. Like, for @babel/runtime to import core-js as /core-js/library/modules or programmatically detect polyfills that are already imported


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babel-bot commented Nov 29, 2018

Hey @lerayne! We really appreciate you taking the time to report an issue. The collaborators
on this project attempt to help as many people as possible, but we're a limited number of volunteers,
so it's possible this won't be addressed swiftly.

If you need any help, or just have general Babel or JavaScript questions, we have a vibrant Slack
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zloirock commented Nov 29, 2018

It's rather an issue for a bundler. You could add a mapping core-js/library -> core-js to webpack. However, you can get some problems with a difference of versions.

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