"undefined is not a function" for CP and didInsertElement

I'm wrapping a JS component into an Ember Addon, something I've done many times before, and yet I'm running into a problem right at the get-go that makes me worry that maybe the "magic" of ember has shifted slightly? Anyway hoping can explain why the following:

import Ember from 'ember';
import layout from '../templates/components/nav-menu';

export default Ember.Component.extend({
  layout: layout,
    tagName: 'nav',
  classNames: ['navmenu','navmenu-default','navmenu-fixed-left'],
  attributeNames: ['role:navigation'],
  classNameBindings: ['offcanvas'],
  hideAt: null,
  offcanvas: function() {
    let hideAt = this.get('hideAt');
    if(!hideAt) {
      return 'offcanvas';
    } else {
      return 'offcanvas-%@'.fmt(hideAt);
    }
  }.property('hideAt'),

  _initialize: function() {
    this.$().offcanvas();
  }.on('didInsertElement')
});

This fails on two counts. As-is it fails in the offcanvas computed property saying:

Uncaught TypeError: undefined is not a function

Very odd but it gets odder. If remove this computed property it then fails at the _initialize() call with the same "undefined is not a function" error:

I'm using Ember 1.11.0, Ember-CLI 0.2.2.