title: How to use Ext.data.writer.Json of Ext-js 4?
body: <p>I have codes reading JSON data from server by a proxy.</p>
  
  <p>But how to write back new data using <code>Ext.data.writer.Json</code>? Any example?</p>
  
  <p>I have a grid pannel associated with a store, which has a proxy I said beyond.</p>
  
  <p>I'll put some code if you need to check out.</p>