title: Check if object exists in an array before pushing
body: <p>I have an empty array and a selectable tree, and every time when the user is checking or un-checking a node I'm pushing the node's id and if the checkbox is true or false.</p>
  
  <p>But right now if the user will check and then un-check a node there will be two objects in the array of the same node how can i make sure that doesn't happen?</p>
  
  <pre><code>//creating empty array
  
  var checkedItems = []; 
  
  //(in kendo observable) on user selection I'm pushing the checked node to array
  
  onItemChecked : function (e) {
      var node = e.sender.dataItem(e.node);
      checkedItems.push({Id: node.Id, IsChecked: node.checked});
  },
  </code></pre>