FWIW, the *leanest* code (does not recreate strings, objects, etc);

Code:
var success_handler = function(response, opts){
        makeRequest();
    },
    failure_handler =  function(){
        makeRequest();
    },
    ajaxCfg = {
       url: 'router.php',
       success: success_handler,
       failure: failure_handler,
       params:  { 
            foo: 'bar' 
        }
    };


function makeRequest(){
    Ext.Ajax.request(ajaxCfg);
}

makeRequest();