オブジェクトの要素数を数える

コード

var obj1= {};
console.log(Object.keys(obj1).length); //0

var obj2= 
{
"0":["東京","1","n1"],
"1":["大阪","2","n2"],
"2":["京都","3","n3"],
"3":["福岡","4","n4"],
"4":["東京","5","n5"],
"5":["東京","7","n6"],
"6":["大阪","1","n7"]
};
console.log(Object.keys(obj2).length); //7