TypeError: Super expression must be null or a function, not undefined with Babeljs

Your export doesn't match your import:

export class Point
// and
import Point from './pointES5'

You're exporting a named symbol but importing the default, so you'll be getting the wrong object as Point in your second file.

You can either use:

export default class Point

in the first class file or

import {Point} from './pointES5';

in the second file to fetch the right reference. If you're going for the single-class-per-file layout, I'd suggest the former. You'll typically only have a single class being exported, so it makes sense to have that as the default.

What you have now is the equivalent of:

// in Point
module.exports = {
  Point: Point
};

// in ColorPoint
var Point = require('./pointES5'); // will point to *the whole object*

class SubPoint extends Point