rendering cfgrid through js

i have a html cfgrid that should be populated by a cfc

to the cfc i'm passing 4 column names and a string (as form field values)

this works fine with a cfinvoke, when page loads first. but now i want to be able to pass different values to cfc and reload my grid with the new values.

i've created a proxy <cfajaxproxy cfc="repfunc" jsclassname="rproxy" />

created a js function:

function srcCxReqs(srcReqs,f1,f2,f3,f4) {

         var instance = new rproxy();

         instance.srcCxReqs(srcReqs,f1,f2,f3,f4);

         ColdFusion.Grid.refresh('testgrid');

     }

created a button that collects (correctly) the values to pass and calls the js function:

<button name="getReqs" onClick="srcCxReqs(getElementById('srcReqs').value, getElementById('f1').options[f1.selectedIndex].value, getElementById('f2').options[f2.selectedIndex].value, getElementById('f3').options[f3.selectedIndex].value, getElementById('f4').options[f4.selectedIndex].value)">

<cfgrid name="testgrid" format="html" query="cxReqs"></cfgrid>

but when i try it, get "Exception thrown and not caught, cfajax.js, Code:0

i'm not even sure the cfajaxproxy is the right way to do it.

does anybody have a working example of a cfgrid being renedered again by a js function?

thanks