title: Extjs 3.4 custom JSONReader
body: <p>I haven't had a question from quite a while, but I finally ended up hitting a wall here. Anyways, to make this easy. I am trying to create a JSON store in extjs 3.4 (work related, and no I am not updating).
  Well, I created the queries as usual with the proper response and fill it up. My problem is that I have 1 extra property on the JSON that I want to be able to pull and use on the app.
  Sample of my JSON from the response object in chrome:</p>
  
  <pre><code>myInventory: [{Priority:1, PMNumber:444, Description:fix-a-tape, Assets:3, Storage_Count:0,…},…]
  percent: 97.040498442368
  totalCount: "3"
  </code></pre>
  
  <p>Now, I know this is correctly formatted because the Grid I am using gets populated, but I can't get the percent property. So my question is, how do you pull an extra parameter on the datastore building block of code when you have one extra parameter that is not usual on EXTjs, in my case the percent?
  I tried doing a metachange on the JSONReader, but all I get is percent:"percent" on the properties as I inspect the datastore after it's creation.</p>