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

 var a = 'hello world';

 var b = 100;

 var c;

 var d = null;

 var e = {

     name : 'My name is Pelli.'

 }

 var f = [100,3,'hello',[4,4,67,'hah'],{age : 34}];

 var g = function(){

     console.log("I am Pelli.");

 }

 console.log(typeof a);//'string'

 console.log(typeof b);//'number'

 console.log(typeof c);//'undefined'

 console.log(typeof d);//'object'

 console.log(typeof e);//'object'

 console.log(typeof f);//'object'

 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

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javascript数据类型判断

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