js 类型判断

1.typeof

　　其他（数字Number，布尔值Boolean，字符串String，函数Function，对象Object，Undefined）这一些数据类型在typeof 下都被精准的解释，只有数组和null的数据类型不够精准。　

console.log(typeof 2);               // number
console.log(typeof true);            // boolean
console.log(typeof 'str');           // string
console.log(typeof []);              // object     []数组的数据类型在 typeof 中被解释为 
console.log(typeof function(){});    // function
console.log(typeof {});              // object
console.log(typeof undefined);       // undefined
console.log(typeof null);  

2.instanceof

　　只有引用数据类型（Array，Function，Object）被精准判断

console.log(2 instanceof Number);                    // false
console.log(true instanceof Boolean);                // false 
console.log('str' instanceof String);                // false  
console.log([] instanceof Array);                    // true
console.log(function(){} instanceof Function);       // true
console.log({} instanceof Object);

3.constructor

console.log((2).constructor === Number);
console.log((true).constructor === Boolean);
console.log(('str').constructor === String);
console.log(([]).constructor === Array);
console.log((function() {}).constructor === Function);
console.log(({}).constructor === Object);　　

4.Object.prototype.toString.call

最靠谱

var a = Object.prototype.toString;
 
console.log(a.call(2));
console.log(a.call(true));
console.log(a.call('str'));
console.log(a.call([]));
console.log(a.call(function(){}));
console.log(a.call({}));
console.log(a.call(undefined));
console.log(a.call(null));

　　

参考 ：https://blog.csdn.net/zjy_android_blog/article/details/81023177