Javascript concatenating numbers, not adding up

Question

It keeps concatenating my numbers into 2111 instead of 5. Why is this? I've tried using parseInt with no luck. res3 btw represents a query into my database that I'm executing.

var dt_total_hours = 0;

            dt_total_hours += res3.fieldByName(dt_cost_per_hour);
            dt_total_hours += res3.fieldByName(dt_prod_dt_hours);
            dt_total_hours += res3.fieldByName(dt_prod_rate);
            dt_total_hours += res3.fieldByName(dt_cost_per_unit);
            dt_total_hours += res3.fieldByName(dt_scrap_startup_cost);
            dt_total_hours += res3.fieldByName(dt_labor_expense);
            dt_total_hours += res3.fieldByName(dt_since_issues_first_noticed);
            dt_total_hours += res3.fieldByName(dt_wo_for_maint);
            dt_total_hours += res3.fieldByName(dt_investigation);
            dt_total_hours += res3.fieldByName(dt_maint_made_bandaid);
            dt_total_hours += res3.fieldByName(dt_parts_outsourcing);
            dt_total_hours += res3.fieldByName(dt_get_equip_out_prod);
            dt_total_hours += res3.fieldByName(dt_perm_repair);
            dt_total_hours += res3.fieldByName(dt_equip_back_to_prod);
            dt_total_hours += res3.fieldByName(dt_to_full_prod_speed);
            dt_total_hours += res3.fieldByName(dt_other);

Answer 1

If the values are strings then they will be concatenated, not added numerically.

Try constructing a number from the string value:

dt_total_hours += Number(res3.fieldByName(dt_cost_per_hour));
//                ^------ Force a number here instead of a string.