Searching webstore category via script?

Would like to do some checks on Webstore products.
What is the field id for Webstore category?

I noticed that it is called itemid as well. Is that correct?

Looking under the List> Website> Categories, I managed to find the internal id of the Category name I want (assuming it is itemid as well)
I wanted to search for all the products that falls under a certain web category, using a script, the following code doesn't seem to work. Help pls....

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function MessageAtCheckout()
{
//get the message from custom field in transaction form
var  msg = nlapiGetFieldValue('custbodycheckout_message');