title: Can't load file in ExtJS if running locally
body: <p>I was running a simple Tree example on my webstorm. In my <strong>Index.html</strong> I had this code which accessed a <strong>treegrid.json</strong> file in the same folder.</p>
  
  <pre><code>    var store = Ext.create('Ext.data.TreeStore', {
          model: 'Task',
          proxy: {
              type: 'ajax',
              //the store will get the content from the .json file
              url: 'treegrid.json'
          },
          folderSort: true
      });
  </code></pre>
  
  <p>I want to be able to have it running just from the file system. So I double clicked the index.html from explorer, but I got this error :</p>
  
  <blockquote>
    <p>file:///C:/developer/eclipse/workspaces/iLean/JS_FrameworkTest/Extjs/test/t…B%22property%22%3A%22leaf%22%2C%22direction%22%3A%22ASC%22%7D%5D&amp;node=root.
    Received an invalid response. Origin 'null' is therefore not allowed
    access.</p>
  </blockquote>
  
  <p>So I decided to put in the full file path, to see if that did anything :</p>
  
  <pre><code>    var store = Ext.create('Ext.data.TreeStore', {
          model: 'Task',
          proxy: {
              type: 'ajax',
              //the store will get the content from the .json file
              url: 'C:\\developer\\eclipse\\workspaces\\iLean\\JS_FrameworkTest\\Extjs\\test\\treegrid.json'
          },
          folderSort: true
      });
  </code></pre>
  
  <p>But this gives the same error.</p>
  
  <p>I am assuming that the <strong>proxy --> type : ajax</strong> setting is wrong. I would assume that there was something like <strong>type : filesystem</strong>, but I can't find any documentation on the ExtJS site.</p>