The stock indexes posted moderate gains Friday as the Nasdaq wrapped up its best weekly percentage gain since mid-July. The Nasdaq tacked on 0.6% Friday, while the S&P 500 added just under 0.4%. The Dow Jones industrial average rose 0.5%. The small-cap S&P 600 led the field with an 0.8% gain. The IBD 50 matched the small-cap index with an 0.8% gain of its own. Volume rose solidly on the NYSE and fell modestly on the Nasdaq.