Uncaught TypeError: Illegal Constructor - Using Bonsai.JS in Backbone.JS

I'm still new to js, ​​and I'm trying to put bonsai.js in the base application.

I follow this guide here: https://github.com/iamdustan/bonsai-demos and try to "Split Everything" by putting the animation in a separate file called hero-animation.js, but I get Uncaught TypeError: Illegal constructorin the first linehero-animation.js

This is called on my Backbone router and it works fine ...

homeAnimation: function() {
    bonsai.run(document.getElementById('heroContent'), {
    url: 'hero-animation.js',
    width: 500,
    height: 400
  });
}

Here is what I have in hero-animation.js, which leads to an error on line 1:

var rect = new Rect(0, 0, 200, 200);
rect
.fill('random')
.addTo(stage)
.attr({
  x: stage.width - rect.attr('width'),
  y: stage.width - rect.attr('height')
})
.animate('0.5s', {
  x: 0,
  y: 0
});