javascript数据类型判断

javascript基本数据类型：原始类型和引用类型

原始类型（简单数据类型）：String，Number，Boolean，Undefined，Null，Symbol（ES6新增）

引用类型（复杂数据类型）：Array，Object

 1 var a = 'hello world';
 2 var b = 100;
 3 var c;
 4 var d = null;
 5 var e = {
 6     name : 'My name is Pelli.'
 7 }
 8 var f = [100,3,'hello',[4,4,67,'hah'],{age : 34}];
 9 var g = function(){
10     console.log("I am Pelli.");
11 }
12 
13 console.log(typeof a);//'string'
14 console.log(typeof b);//'number'
15 console.log(typeof c);//'undefined'
16 console.log(typeof d);//'object'
17 console.log(typeof e);//'object'
18 console.log(typeof f);//'object'
19 console.log(typeof g);//'function'

关键方法：typeof,instanceof,constructor,prototype

关键点：

typeof判断的结果，返回值肯定是字符串
typeof判断的结果的返回值一定在以下六个之中，ES6（也称为ES2015）之后新增一个，一共七个
typeof 判断的返回值：string,number,boolean,function,object,undfined,symbol
instanceof运算符详解，参考链接：http://www.zuojj.com/archives/393.html
instanceof运算符可以用来判断某个构造函数的prototype属性是否存在另一个要检测对象的原型链上
instanceof后面的操作数必须是一个对象
继承中判断实例是否属于它的父类
constructor：构造函数；每个对象都有一个constructor属性，指向该对象的构造函数；
prototype:每个对象都有一个prototype属性，指向该对象的原型对象。

数据类型判断方法：

typeof方法，见上面部分代码；

instanceof方法：返回true或false，适用于引用类型，不适合基本数据类型

var x = [1,2,3,"Pelli","Hello World"];
var y = {
	year : 2016,
	month : 8
}
var z = function(){}

var z1 = 'hello';
var z2 = 123;
var z3 = true;
var z4 = null;
var z5 = undefined;

console.log(x instanceof Array);//true
console.log(y instanceof Object);//true
console.log(z instanceof Function);//true

console.log(z1 instanceof String);//false
console.log(z2 instanceof Number);//false
console.log(z3 instanceof Boolean);//false
console.log(z4 instanceof Object);//false
console.log(z5 instanceof Object);//false

constructor：

var a1 = 'Pelli';
var a2 = 200;
var a3 = true;
var a4 = null;
var a5 = undefined;
var a6 = {}
var a7 = [1,2];
var a8 = function(){}

console.log(a1.constructor === String);//true
console.log(a2.constructor === Number);//true
console.log(a3.constructor === Boolean);//true
console.log(a4.constructor === Object);//Uncaught TypeError:Cannot read property 'constructor' of null...
console.log(a5.constructor === Object);//Uncaught TypeError:Cannot read property 'constructor' of undefined...
console.log(a6.constructor === Object);//true
console.log(a7.constructor === Array);//true
console.log(a8.constructor === Function);//true

prototype

var a1 = 'Pelli';
var a2 = 200;
var a3 = true;
var a4 = null;
var a5 = undefined;
var a6 = {}
var a7 = [1,2];
var a8 = function(){}
console.log(Object.prototype.toString.call(a1) === "[object String]");//true
console.log(Object.prototype.toString.call(a2) === "[object Number]");//true
console.log(Object.prototype.toString.call(a3) === "[object Boolean]");//true
console.log(Object.prototype.toString.call(a4) === "[object Null]");//true
console.log(Object.prototype.toString.call(a5) === "[object Undefined]");//true
console.log(Object.prototype.toString.call(a6) === "[object Object]");//true
console.log(Object.prototype.toString.call(a7) === "[object Array]");//true
console.log(Object.prototype.toString.call(a8) === "[object Function]");//true