JavaScript で週の計算

　JavaScript を用いて，月の第n週目や第mのx曜日を求める方法です。

テスト実行

function getWeeks () { var weekdays = [ "日", "月", "火", "水", "木", "金", "土" ]; var today = new Date(); var out = "今日は "+ (today.getMonth() + 1) + " 月の\n"; out += "第" + Math.floor((today.getDate() + 6 ) / 7) + weekdays[today.getDay()] + "曜日\n"; out += "第" + Math.floor((today.getDate() - today.getDay() + 12 ) / 7) + "週目\n"; alert (out); }