discourse/app/assets/javascripts/wizard/controllers/application.js

import Controller from "@ember/controller";
import discourseComputed from "discourse-common/utils/decorators";

export default Controller.extend({
  currentStepId: null,

  @discourseComputed("currentStepId")
  showCanvas(currentStepId) {
    return currentStepId === "finished";
  },

  @discourseComputed("model")
  fontClasses(model) {
    const fontsStep = model.steps.findBy("id", "fonts");
    if (!fontsStep) {
      return [];
    }

    const fontField = fontsStep.get("fieldsById.font_previews");
    return fontField.choices.map(choice => `font-${choice.data.class}`);
  }
});