js 判断数据类型、检测变量类型、对象的类型（typeof）

//typeof，返回变量类型
typeof(1);  //返回："number"
typeof(NaN);  //返回："number"
typeof(Number.MIN_VALUE);  //返回："number"
typeof(Infinity);  //返回："number"
typeof("123");  //返回："string"
typeof(true);  //返回："boolean"
typeof([1,2,3]);  //返回："object"
typeof([]);  //返回："object"
typeof({"a":1,"b":2});  //返回："object"
typeof(window);  //返回："object"
typeof(document);  //返回："object"
typeof(null);  //返回："object"
typeof(eval);  //返回："function"
typeof(Date);  //返回："function"
typeof(sss);  //返回："undefined"
typeof(undefined);  //返回："undefined"

//实例
var test = function(){ var a=1; };
if(typeof test == 'function'){
	alert('这是一个function类型');
}