https://stackoverflow.com/questions/45462485/how-to-remove-class-from-other-elements-in-emberjs

controllers.application.js

import Ember from 'ember';
export default Ember.Controller.extend({  
  selectedIndex:undefined,
  actions:{
    changeSelectedIndex(index){
      this.set('selectedIndex',index);
    }
  }
});

routes.application.js

import Ember from 'ember';
export default Ember.Route.extend({
  model(){
    return [1,2,3,4];
  }
});

styles.app.css

body {
  margin: 12px 16px;
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 12pt;
}
.highlight{
  border:1px solid red;
}

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<div class="parent">
  <ul>
  {{#each model as | temp index|}}
    <li class={{if (eq selectedIndex index) 'highlight' }} {{action 'changeSelectedIndex' index}}>{{temp}}</li>
 {{/each}}   
  </ul>
</div>
<br>
{{outlet}}
<br>
<br>

twiddle.json

{
  "version": "0.12.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.7.3",
    "ember-template-compiler": "2.7.3",
    "ember-testing": "2.7.3"
  },
  "addons": {    
    "ember-truth-helpers": "1.3.0"
  }
}