Returning data from Ajax call in Ext.onReady

I have an Ext JS app and I want to check on the backend if the session is invalid every time a user clicks on a link within the app. These two Ajax calls are both in Ext.onReady, I would like to clean up this code but I need to check for timeout every click, the second Ajax call is only called upon logging in if it were by itself. This is in my app.js also.

Code:

Ext.Ajax.on('requestcomplete', function(conn, response, options, options) {    
    if(!isSessionValid()) {        
       window.location.href = '?login_status=timeout';    
   }
});

function isSessionValid() {    
    Ext.Ajax.request({        
        url: contextRoot + '/isSessionValid.htm?alt=json',        
        method: 'get',        
        success: function(response, options) {            
            console.log(response);            
            var isValid;            
            var o = Ext.decode(response.responseText);            
            (o != loggedInUser.username) ? isValid = false : isValid = true;           
            return isValid;        
        }, 
        failure: function(response, options) {            
            //console.log(response);        
        }    
    });
}

Obviously isSessionValid will return undefined.. is there a workaround to get the data I need and not have my ajax call continuously calling?