Babel error: Class constructor Foo cannot be invoked without 'new'

Another solution is to include { exclude: ["transform-es2015-classes"] } in .babelrc

presets: [
   ["env", { exclude: ["transform-es2015-classes"] }]
]

UPDATE: In the latest version of "env" preset plugin names have changed (e.g. it's now "transform-classes"). Use the "debug" option to inspect which plugins are included.

Due to the way ES6 classes work, you cannot extend a native class with a transpiled class. If your platform supports native classes, my recommendation would be, instead of using the preset es2015, use es2015-node5, assuming you're on Node 5. That will cause Babel to skip compiling of classes so that your code uses native classes, and native classes can extend other native classes.