jquery怎样判断是否是字符串

var str="ss";
alert((typeof str=='string')&&str.constructor==String)

var obj=[0];
alert((typeof obj=='object')&&obj.constructor==Array)

function isString(obj){ //判断对象是否是字符串  
   return Object.prototype.toString.call(obj) === "[object String]";  
}  
验证：
var str1 = 'abc';
var str2 = new String('abc');
 
typeof str1; //"string"
typeof str2; //"object"
Object.prototype.toString.call(str1); //"[object String]"
Object.prototype.toString.call(str2); //"[object String]"

var str=547.97;
alert((typeof str=='number')&&str.constructor==Number)

var obj =new Date();
alert((typeof obj=='object')&&obj.constructor==Date)

var obj = function test(){};
alert((typeof obj=='function')&&obj.constructor==Function)