Is quantityavailable available to client scripts?

I am working on a client script that depends upon a inventory parts having quantity available in a certain location.

I have a similar script working as a user event, however in trying to access quantityavailable via a client script I am returning null.

The following code illustrations the issue:

    var numLocations = nlapiGetLineItemCount('locations');
    alert('num locations: ' + numLocations);
    for (l = 1; l <= numLocations; l++)
    {     
        tQty = nlapiGetLineItemValue('locations', 'quantityavailable', l);
        alert(tQty);
    }

A word of caution: if you have a number of locations, you're going to get a popup for each one.

Can anyone explain why I am always returning null with this? Or are these fields not available on client side?