title: Use indexOf method with Vuejs
body: <p>I have a method in my vue js element:</p>
  
  <pre><code>_deleteDesign : function(dsn)
  {
      //_deleteDesign
      var url = '{{ url('/fapi/designsTmp/') }}/'+dsn.design_id;
      axios.delete(url)
      .then(function(){ 
          this.$delete(this.creations, this.creations.indexOf(function(el){
              return el.design_id = dsn.design_id;
          }));
      })
      .catch(function(e){
          alert('error deleting design');
      })
      debugger;
  }
  </code></pre>
  
  <p>In this method I am using the <strong>indexOf</strong> function of Javascript, but vuejs reports me this error in the Chrome debugger:</p>
  
  <p><strong>this.creations.indexOf is not a function</strong></p>
  
  <p>What's the problem?</p>