js判断数据类型

在js中如果想判断某种数据的数据类型，一般使用typeof方法

            var str = "string";
            var num = 1;
            var bool = true;
            var u;
            var n = null;
            var nan = NaN;
            var obj = new Object();
　　　　     var fn = function () {};
            
            console.log(typeof str); //string
            console.log(typeof num); //number
            console.log(typeof bool); //boolean
            console.log(typeof u); //undefined
            console.log(typeof n); //object
            console.log(typeof nan); //number
            console.log(typeof obj); //object
            console.log(typeof fn); //function

注：NaN的类型是number

 

但是如果是数组、对象或者正则用typeof方法则无法区分

            var arr = [1,2];
            var obj = {};var reg = /^\d{11}$/;
            
            console.log(typeof arr); //object
            console.log(typeof obj); //object
            console.log(typeof reg); //object

 

因为所有引用类型的值都是Object的实例，所以要判断引用类型的具体数据类型要使用instanceof方法:

            var arr = [1,2];
            var obj = {};
            var reg = /^\d{11}$/;
            
            console.log(arr instanceof Array) //true
            console.log(obj instanceof Object); //true
            console.log(reg instanceof RegExp); //true