<script>
var obj = {};
console.log(obj);
var obj2 = [];
console.log(obj2);
var obj3;
console.log(obj3);
</script>
打印如下：
Object
Array[0]
undefined
var obj = {};var obj2 = [];var obj3;
原文：http://www.cnblogs.com/jackiehe/p/4338041.html