Externalize references to helpers using babel-helper-modules-es3.
If you want to externalize builtins too via core-js's library, see the official plugin babel-plugin-transform-runtime.
$ npm install babel-plugin-transform-es3-helper-modules babel-helper-modules-es3
Remember to also install babel-helper-modules-es3. when using the transpiled code.
.babelrc
{
"plugins": ["transform-es3-helper-modules"]
}
$ babel --plugins transform-es3-helper-modules script.js
require("babel-core").transform("code", {
plugins: ["transform-es3-helper-modules"]
});