stackoverflow question#43259278

components.failure-cell.js

import Ember from 'ember';

export default Ember.Component.extend({
  tagName: 'td',
  isFailure: Ember.computed.equal('resultDetail.failures', 0),
  classNameBindings: ['isFailure:alert', 'isFailure:alert-danger']
});

components.my-component.js

import Ember from 'ember';

export default Ember.Component.extend({
})

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  
  resultsDetail: [{samples: 10, failures: 0}, {samples: 20, failures:1}],
  
  actions: {
    changeFirstResultsFailure() {
      let firstResult = this.get('resultsDetail')[0];
      
      if (firstResult.failures === 0) {
        Ember.set(firstResult, 'failures', 1);
      } else {
        Ember.set(firstResult, 'failures', 0);
      }
    }
  }
});

helpers.td-class-assigner.js

import Ember from 'ember';

export function tdClassAssigner(params/*, hash*/) {
  let resultDetail = params[0];
  
  
  return params;
}

export default Ember.Helper.helper(tdClassAssigner);

styles.app.css

body {
  margin: 12px 16px;
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 12pt;
}

.alert-danger {
  background-color: #FF0000
}

table, th, td {
  border: 1px solid black;
}

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
{{my-component resultsDetail=resultsDetail}}
<br>
<br>

<button onclick={{action 'changeFirstResultsFailure'}}>Change First Result's Failure to update td classes</button>

templates.components.failure-cell.hbs

{{resultDetail.failures}}

templates.components.my-component.hbs

 <tbody>
        {{#each resultsDetail as |resultDetail|}}
        <tr>
           <td>
                {{resultDetail.samples}}
            </td>
            {{failure-cell resultDetail=resultDetail}}
          </tr>
        {{/each}}
</tbody>

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": "2.12.0",
    "ember-template-compiler": "2.12.0",
    "ember-testing": "2.12.0"
  },
  "addons": {
    "ember-data": "2.12.1"
  }
}