How to iterate over class variables from Handlebars in ember-cli?

I'd like to iterate over a class variable array in Handlebars in ember-cli to generate a list of checkboxes (categories), with the appropriate ones checked off based on which categories the model belongs to.

I have several issues: - I can't figure out how to access the class variable in ember-cli. I've seen tutorials showing that in ember.js, it's just App.Listing.CATEGORIES, but I'm not getting any passes through my each loop. - How to check off the appropriate box? I have some janky code below that probably doesn't work.

listing.js:

import DS from "ember-data";

var Listing = DS.Model.extend({
    categories: DS.attr(), // string array
});

Listing.reopenClass({
    CATEGORIES: ['park', 'outdoors']
});

export default Listing;

show.hbs:

<ul>
{{#each category in CATEGORIES}}
<li>{{input type="checkbox" name=category checked=categories.contains(category)}} {{category}}</li>

{{/each}}
</ul>