title: How to custom sort grid using two parameters?
body: <p>I want to make custom sorting for the grid so that the data/items which have negative <code>id</code> be always placed on top, and the rest should be sorted depending on the selected column (<code>dataIndex</code>)</p>
  <p>I have tried to use <code>sortFn</code> in <code>columns</code> but don't know how to proceed. If I return the value then it won't affect sorting by <code>name</code> (in this example).</p>
  <pre><code>{
          text: 'Name',
          zwidth: 150,
          autoSizeColumn: true,
          sortable: true,
          hideable: true,
          dataIndex: 'name',
          sorter: {
              sorterFn: function (a, b) {
                  if (a.id &lt; 0 || b.id &lt; 0)
                  // how to put them in first two positons and rest sort by 'name'
              }
          }
      }
  </code></pre>
  <p>The whole example could be found here in this fiddle.</p>
  <p><a href="https://fiddle.sencha.com/#view/editor&amp;fiddle/3kqi" rel="nofollow noreferrer">https://fiddle.sencha.com/#view/editor&amp;fiddle/3kqi</a></p>
  <p>I am using ExtJS 6.</p>