Sometimes you want to override one of the methods in ExtJS that return a configuration object - let's use Ext.direct.RemotingProvider's getCallData as an example, which looks like this:

getCallData: function(t){
  return {
    action: t.action,
    method: t.method,
    data  : t.data,
    type  : 'rpc',
    tid   : t.tid
  };
}

Our aim is to add an 'authentication_token' property to the returned object. You could provide the full config object again in an override, but usually you're overriding to add, remove or change one or two properties and want to leave the rest unmolested. I used to find myself writing a lot of code with this pattern:

//just adds an authentication token to the call data, for context see <a href="http://www.extjs.com/forum/showthread.php?p=378912#post378912">this forum thread</a>
(function() {
  var originalGetCallData = Ext.direct.RemotingProvider.prototype.getCallData;
  
  Ext.override(Ext.direct.RemotingProvider, {
    getCallData: function(t) {
      var defaults = originalGetCallData.apply(this, arguments);
      
      return Ext.apply(defaults, {
        authenticity_token: '<%= form_authenticity_token %>'
      });
    }
  })
})();