typeof与instanceof
判断字符串类型可用typeOf，但判断数组，对象，正则，null时，返回的都是Object,所以可用instanceof来判断类型
<script>var str = 'Lee';alert(typeof str);//stringvar arr = [1,2,3];alert(typeof arr);//objectalert(arr instanceof Array);//true</script>
注意：当类型为string时，用 instanceof 判断的话会为 false
<script>var str = 'xu xiao dai';alert(str instanceof String);//falsevar strObj = new String('xu xiao dai');alert(strObj instanceof String);//true</script>