title: isCancel is always false in axios
body: <p>i am trying to cancel a post request in <code>axios</code>  which is a file upload
  but when i tried to use <code>axios.isCancel()</code> it's returning always false
  although  when i checked the <code>cancel token</code> object after canceling it says <code>promise fulfilled</code> that means it's canceled right ?<br />
  this is my js code :</p>
  <pre class="lang-js prettyprint-override"><code>const CancelToken = axios.CancelToken;
       const source = CancelToken.source();
       const csrftoken = Cookies.get('csrftoken');
       const formData = new FormData();
       const file_selector= document.getElementById('file-selector');
       const cancel =document.getElementById('cancel');
       const success_server= document.getElementById('mession-complated!');
       const progessbar= document.getElementById('progress');
       file_selector.addEventListener('change', () =&gt; {
       for (let i = 0; i &lt; file_selector.files.length; i++) {
        formData.append(&quot;file&quot;, file_selector.files[i]);
       }
  
       axios.request( {
          method: &quot;post&quot;, 
          url: &quot;upload/&quot;, 
          data: formData,
          headers: {'X-CSRFToken': csrftoken},
          CancelToken: source.token,
          onUploadProgress: (p) =&gt; {
            cancel.style.display= &quot;block&quot; ;
            progessbar.style.display= &quot;block&quot; ;
            progessbar.value= Math.round( (p.loaded * 100) / p.total );
            if(progessbar.value==100){
            cancel.style.display= &quot;none&quot; ;
            progessbar.style.display= &quot;none&quot; ;
            }
             
            //this.setState({
              //fileprogress: p.loaded / p.total
            //})
          }
  
          
        }).then (() =&gt; {
         console.log(source.token);
  
        if (axios.isCancel()) {
          console.log('Request canceled');
      }})
    
         
  
      
  
  
  
  
  
  
       })
  
       function cancel_upload(){
        source.cancel('Operation canceled');
       }
  </code></pre>