How to access model instance from function in model?

I wrote a function inside one of my Ember models that's designed to set some properties on the model instance. Below is a gross over-simplification of what the function is trying to do.

// In widget.js

export default DS.Model.extend({
  ...
  turnOn() {
    this.set('enabled', true);
  }
});

I come from a Ruby background, so something like this feels very natural and appropriate, but I can't seem to access the model instance from within the turnOn() function. Am I doing something wrong? Is there a more appropriate way to accomplish what I'm trying to do?