js判断是否为空和typeof的用法

(1)typeof作用
用于查看数据类型

(2)typeof用法
typeof 返回值类型有number, string, boolean, function, undefined, object
PS:在使用typeof()操作符时圆括号是可选项,可带可不带。即两种形式 typeof(XX) 或 typeof XX

1  console.log(typeof 2); // number
2  console.log(typeof "2"); // string
3  console.log(typeof true); // boolean
4  console.log(typeof [2]); // object
5  console.log(typeof {name:2});// object
6  console.log(typeof function(){return 2});// function
7  console.log(typeof new Date());// object
8  console.log(typeof null); // object
9  console.log(typeof undefined);// undefined

但typeof只能区分number, string, boolean, function及undefined,其他的对象、数组、日期、null等都返回Object,存在缺陷。
利用Object.prototype.toString.call可以很好的区分各种类型(注:无法区分自定义对象类型,自定义类型可以采用instanceof区分)

 1 console.log(Object.prototype.toString.call("zhangsan"));//[object String]
 2 console.log(Object.prototype.toString.call(12));//[object Number]
 3 console.log(Object.prototype.toString.call(true));//[object Boolean]
 4 console.log(Object.prototype.toString.call(undefined));//[object Undefined]
 5 console.log(Object.prototype.toString.call(null));//[object Null]
 6 console.log(Object.prototype.toString.call({name: "zhangsan"}));//[object Object]
 7 console.log(Object.prototype.toString.call(function(){}));//[object Function]
 8 console.log(Object.prototype.toString.call([]));//[object Array]
 9 console.log(Object.prototype.toString.call(new Date));//[object Date]
10 console.log(Object.prototype.toString.call(/\d/));//[object RegExp]
11 function Person(){};
12 console.log(Object.prototype.toString.call(new Person));//[object Object]

(3)js判断是否为空

1 var exp = null; 
2 if (!exp && typeof(exp)!="undefined" && exp!=0 && exp!='') 
3 { 
4   alert("is not null"); 
5 } 

 

转载于:https://www.cnblogs.com/xmm2017/p/11470323.html

你可能感兴趣的:(js判断是否为空和typeof的用法)