In November 2015, I was writing that decorators had been ripped out of Babel 6.

Now, they are back. Install babel-plugin-transform-decorators-legacy and update .babelrc to include the legacy decorators transform:

{
  "presets": ["stage-0", "es2015", "react"],
  "plugins": ["transform-react-display-name", "transform-decorators-legacy"]
}

I can now use an @foo decorator to wrap a class and add a bar() method to it:

// The @foo decorator is just a function
function foo (x) {
  return class Bar extends x {
    name () {
      return 'bar';
    }
  };
}


// Apply the decorator to class Foo...
@foo
class Foo {
  name () {
    return 'foo';
  }
}

const foo = new Foo ();

// Foo is in fact Bar
expect (foo.name ()).to.equal ('bar');