title: ExtJS 5 - Add a key/value to Object in Mixed Collection
body: <p>I have a mixed Collection Object, which have 5 items in it. Based on certain condition now i would like to add a new set of key/value pair to one of the item.</p>
  
  <pre><code>items: Array[5]
    0: Object$extCollectionIndex: 2
    align: "left"
    dataIndex: "reportCode"
    hidden: false
    hideable: true
    sortable: true
    sorted: false
    text: "Report Code"
    width: 74
    xtype: null
    __proto__: Object
    1: Object
    2: Object
    3: Object
  </code></pre>
  
  <p>It it achievable in Mixed Collection ? </p>
  
  <p>Thanks!</p>