title: Angular - ngx-translate - Checking if translate key exist with Angular
body: <p>I use ngx-translate in my Angular application.</p>
  
  <p>My HTML template:</p>
  
  <pre><code>&lt;span [ngClass]="(role === 'ADMIN') ? 'badge badge-danger' : 'badge badge-success'"&gt;{{ 'ADMIN.USER.ROLES.' + role | translate }}&lt;/span&gt;
  </code></pre>
  
  <p>My i18n json file:</p>
  
  <pre><code>"ADMIN": {
    "USER": {
      "ROLES": {
        "ADMIN": "Administrator",
        "FOO": "Auditor FOO",
        "DOO": "Auditor DOO",
        "ROO": "Auditor ROO",
        "unknown": "Unknown"
      }
    }
  }
  </code></pre>
  
  <p>If my role is <code>BIPBIP</code>, I want use 'ADMIN.USER.ROLES.unknown' key.</p>
  
  <p>I looking for a HTML template solution (<strong>NOT Javascript</strong>):</p>
  
  <pre><code>this._translateService.get("app.key").subscribe(res=&gt;{
      if(...) {
          // message does not exist
      }
      else {
          // message exists
      }
  }))
  </code></pre>