You do actually have a 'return' in your js code right?
You might test with something simple like
function donothing() {
return 10;
}
After the mobilecontroldo it the result should be 10.
If you ARE returning a value, you might simplify and make sure you aren't
returning nothing. I THINk that if the code is failing you would get an
error in the result, but not sure.