A script for erpnext to generate the next item ID in the specified product group.

gistfile1.txt

cur_frm.cscript.next_id = function(doc)
    {
    doc.item_code = "";
    var pattern = "";
    pattern = doc.item_group.substring(0,4)+'%';

    var query = "SELECT `tabItem`.name FROM `tabItem` WHERE `tabItem`.name LIKE '" + pattern + "' ORDER BY name desc limit 1";

    wn.call({
    method: "webnotes.widgets.query_builder.runquery",
    args: {
        "query": query
        },
    callback: function(r)
        {
        // returned last value
        var last_id = "";
        if (typeof r != 'undefined' && typeof r.values != 'undefined' && typeof r.values[0] != 'undefined')        
            {
           last_id = r.values[0][0];
            }
        else
            {
            last_id = pattern.substring(0,pattern.length-1) + "001000";
            }

        var last_number = parseInt(last_id.substring(4))+1;
        var new_prefix = last_id.substring(0,4);
        var new_suffix = last_number.toString();
        var new_id = new_prefix;
        for (var i=0;i<(6-new_suffix.length);i++)
            { 
            new_id += '0';
            }
        new_id += new_suffix;
        cur_frm.set_value("item_code", new_id);
        }
    });
    }