Can I add es6 files not in src to transpile so that it can support old version browser in vue project?

Hi, all!

Recently I take over a vue project that contains other es6 files in public folder. They are just simply import by using tags in index.html.

And now I need to make the project support the old version browsers that don’t support es6. After modifying the browserslist, I find that the babel transpile the es6 files into es5 files except those in public folder. Is there a way to modify vue.config.js or babel.config.js to make the es6 files in public folder transpile into es5 files when running the build command? Thanks a lot!