babel/packages/babel-plugin-transform-es2015-unicode-regex/src/index.js

import rewritePattern from "regexpu/rewrite-pattern";
import * as regex from "babel-helper-regex";

export default function () {
  return {
    visitor: {
      RegexLiteral({ node }) {
        if (!regex.is(node, "u")) return;
        node.pattern = rewritePattern(node.pattern, node.flags);
        regex.pullFlag(node, "u");
      }
    }
  };
}