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var date = {
    "2012": ["1"],
    "2011": ["12", "11", "10", "9"],
    "2008": ["12", "11", "10", "9"],
    "2006": ["12", "11", "10", "9"],
    "2007": ["12", "11", "10", "9"],
    "2010": ["12", "11", "10", "9"],
    "2004": ["12", "11", "10", "9"],
    "2005": ["12", "11", "10", "9"]
};

for (var i in date) {
    document.write( i + ' : ' + date[i] + '<br />')
}

<!DOCTYPE html>
<html lang="ja">
<head>
    <meta charset="UTF-8">
    <title>Chrome16やIE9でオブジェクトのプロパティ名が数字の場合昇順にソートされるけど仕様でしょうか？</title>
</head>
<body>

</body>
</html>