在javaScript中檢測數據類型的幾種方式

類型檢測的方法

1. typeof

2. instanceof

3. Object.protype.toString

4. constructor

5. duck type:鴨子類型

typeof

返回一個字符串，適合函數對象和基本類型的判斷

var a = 123; var b = '123'; var c = false; var d = null; var e = undefined; var f = {}; var g = function(){}; var h = []; var i = NaN; console.log(typeof a); console.log(typeof b); console.log(typeof c); console.log(typeof d); console.log(typeof e); console.log(typeof f); console.log(typeof g); console.log(typeof h); console.log(typeof i); 

instanceof

返回一個布爾值，判斷對象類型（基於原型鏈的方式）

原理：
左邊對象的原型鏈（_proto_原型）上是否有右邊構造函數的prototype對象屬性

var a = 123; var b = '123'; var c = false; var d = null; var e = undefined; var f = {}; var g = function(){}; var h = []; var i = NaN; console.log(a instanceof Number); console.log(b instanceof String); console.log(c instanceof Boolean); console.log(d instanceof Object); console.log(e instanceof Object); console.log(f instanceof Object); console.log(g instanceof Function); console.log(h instanceof Array); console.log(i instanceof Number);//NaN是基本類型

這麼多false就說明instanceof不適合用於基本數據類型！！

Object.prototype.toString

var oP = Object.prototype, toString = oP.toString; console.log(toString.call(123));//[object Number] console.log(toString.call('123'));//[object String] console.log(toString.call(false));//[object Boolean] console.log(toString.call(undefined));//[object Undefined] console.log(toString.call(null));//[object Null] console.log(toString.call({a: '123'}));//[object Object] console.log(toString.call(/123/));//[object RegExp] console.log(toString.call([123]));//[object Array] console.log(toString,call(Date));//[object Function] 

注意：IE6/7/8 Object.prototype.toString.call(null/undefined)返回的是[object Object]

constructor

var a = 123; var b = '123'; var c = false; var d = null; var e = undefined; var f = {}; var g = function(){}; var h = []; var i = NaN; console.log(a.constructor == Number); console.log(b.constructor == String); console.log(c.constructor == Boolean); // console.log(d.constructor == Object); // console.log(e.constructor == Object); console.log(f.constructor == Object); console.log(g.constructor == Function); console.log(h.constructor == Array); console.log(i.constructor == Number);