babel-polyfillとbabel-runtimeの使い分けに迷ったので調べた ref: https://qiita.com/terrierscript/items/d2a9d5d4daedaacff924

after.js

(0, _entries2.default)({
    "foo": "baz"
});

before.js

Object.entries({"foo": "baz"})

file2.js

import "babel-polyfill"

file3.html

<!-- どっちも import "babel-polyfill" しているとすると・・・ -->
<script type="text/javascript" src="./script1.js">
</script>
<script type="text/javascript" src="./script2.js">
</script>

file3.js

Object.entries({"foo": "baz"})

file4.html

<!-- どっちも import "babel-polyfill" しているとすると・・・ -->
<script type="text/javascript" src="./script1.js">
</script>
<script type="text/javascript" src="./script2.js">
</script>

file4.txt

Uncaught Error: only one instance of babel-polyfill is allowed

file5.txt

Uncaught Error: only one instance of babel-polyfill is allowed