onBeforeSearchRequest

fires before a search request is sent to the server-side (see details here)

boolean onBeforeSearchRequest(string id,string params){ ... };

id	string	the id of the folder to search in
params	string	the request parameters

boolean

returning false will prevent the operation

$$("fmanager").attachEvent("onBeforeSearchRequest",function(id, params){
    // your code
    return true;
});