let registry = {}; class TransitionController { create(navCtrl, opts = {}) { let name = opts.animation || 'ios'; let TransitionClass = registry[name]; if (!TransitionClass) { TransitionClass = registry['none']; } return new TransitionClass(navCtrl, opts); } register(name, transitionClass) { registry[name] = transitionClass; } } export let Transition = new TransitionController();