javascript 判断数据类型的几种方法

谁借莪１个温暖的怀抱￠ 2022-03-18 20:20 249阅读 0赞

**javascript 判断数据类型的几种方法**  
***一、typeof 直接返回数据类型字段，但是无法判断数组、null、对象***

typeof 1
    "number"
    
    typeof NaN
    "number"
    
    typeof "1"
    "string"
    
    typeof true
    "boolean"
    
    typeof undefined
    "undefined"
    
    typeof null
    "object"
    
    typeof []
    "object"
    
    typeof {}
    "object"

***其中 null, \[\], \{\}都返回 "object"***

**二、instanceof 判断某个实例是不是属于原型**

// 构造函数
    function Fruit(name, color) {
        this.name = name;
        this.color = color;
    }
    var apple = new Fruit("apple", "red");
    
    // (apple != null)
    apple instanceof Object  // true
    apple instanceof Array   // false

**三、使用 Object.prototype.toString.call()判断**

call()方法可以改变this的指向，那么把Object.prototype.toString()方法指向不同的数据类型上面，返回不同的结果

Object.prototype.toString.call(1)
    "[object Number]"
    
    Object.prototype.toString.call(NaN);
    "[object Number]"
    
    Object.prototype.toString.call("1");
    "[object String]"
    
    Object.prototype.toString.call(true)
    "[object Boolean]"
    
    Object.prototype.toString.call(null)
    "[object Null]"
    
    Object.prototype.toString.call(undefined)
    "[object Undefined]"
    
    Object.prototype.toString.call(function a() {});
    "[object Function]"
    
    Object.prototype.toString.call([]);
    "[object Array]"
    
    Object.prototype.toString.call({});
    "[object Object]"

**最后我们可以定义一个完美的判断数据类型的方法 \_typeof()**

function _typeof(obj){
      var s = Object.prototype.toString.call(obj);
      return s.match(/\[object (.*?)\]/)[1].toLowerCase();
    };
    
    
    _typeof([12,3,343]);
    "array"
    
    _typeof({name: 'zxc', age: 18});
    "object"
    
    _typeof(1);
    "number"
    
    _typeof("1");
    "string"
    
     _typeof(null);
    "null"
    
    _typeof(undefined);
    "undefined"
    
    _typeof(NaN);
    "number"
    
    _typeof(Date);
    "function"
    
    _typeof(new Date());
    "date"
    
    _typeof(new RegExp());
    "regexp"

来源：[https://segmentfault.com/a/1190000018160547][https_segmentfault.com_a_1190000018160547]

[https_segmentfault.com_a_1190000018160547]: https://segmentfault.com/a/1190000018160547