title: Ext JS - How to get success property in custom json result object when i load store
body: <p>When I store load, how can I get the success property??</p>
  
  <p>load store: </p>
  
  <pre><code>store.load({
  scope: this,
  callback: function(records, operation, success) {
      if (success) {
          console.log('success');
      } else {
          console.log('error');
      }
  });
  </code></pre>
  
  <p>return json data:</p>
  
  <pre><code>{
  "header" : {
      "success" : "true",
      "message" : "complete!"
  },
  "data" : [{
              "id" : 1,
              "userId" : 1,
              "subject" : "Document 1"
          },{
              "id" : 2,
              "userId" : 1,
              "subject" : "Document 2"
          }]}
  </code></pre>
  
  <p>I want get "success" property in "header" and use this in a condition of the if statement. </p>