Getting element by ID in Ember

I'm new to ember, and I have a very simple question.

I am running two ember applications. On has the following component:

import Ember from 'ember';

export default Ember.Component.extend({
 tagName: 'a',

 click: function() {
  Ember.$('#wrapper').toggleClass('toggled');
 }
});

and another one, has this one:

import Ember from 'ember';

export default Ember.Component.extend({
 tagName: 'a',

 click: function() {
  this.$('#wrapper').toggleClass('toggled');
 }
});

What I can't understand here, is why in one application I select an element by ID using Ember.$('#wrapper') and in the other this.$('#wrapper').

What is it about? Ember version?

Thanks in advance!