title: JSONP not working on ExtJS 4 - Uncaught TypeError: Cannot call method 'substring' of undefined
body: <p>I'm stuck with this code, I'm getting this json formated data from the Youtube API, if I use type:'json' it will fail, because of that cross domain thing but the other elements loads anyway; then, if I change type: to 'jsonp' (which is the syntax described on the ExtJS API) it would give me this error:"Uncaught TypeError: Cannot call method 'substring' of undefined" I tried setting type:'anyotherstupidthing' and the same happens, so what could be happening? </p>
  
  <p>Here are my current data model and my store:</p>
  
  <pre><code>Ext.define('Video', {
      extend: 'Ext.data.Model',
      fields: ['id', 'title']
  });
  
  myStore2 = Ext.create('Ext.data.Store', {
      model: 'Video',
      proxy: {
          type: 'ajax',
          url : 'http://gdata.youtube.com/feeds/api/videos?q=surfing&amp;v=2&amp;alt=jsonc',
          reader: {
              type: 'jsonp',
              root: 'items'
          }
      }
  });
  </code></pre>
  
  <p>Thanks in advance! 
  Ed.</p>