code: function(callback, scope, args, delay){
          if(Ext.isFunction(callback)){
              args = args || [];
              scope = scope || window;
              if (delay) {
                  Ext.defer(callback, delay, scope, args);
              } else {
                  callback.apply(scope, args);
              }
          }
      }
docs: Execute a callback function in a particular scope. If no function is passed the call is ignored.
  
  For example, these lines are equivalent:
  
  Ext.callback(myFunc, this, [arg1, arg2]);
  Ext.isFunction(myFunc) && myFunc.apply(this, [arg1, arg2]);
  
  @param {Function} callback The callback to execute
  @param {Object} [scope] The scope to execute in
  @param {Array} [args] The arguments to pass to the function
  @param {Number} [delay] Pass a number to delay the call by a number of milliseconds.