详解JavaScript中的4种类型识别方法

具体内容如下：

1.typeof

【输出】首字母小写的字符串形式

【功能】

[a]可以识别标准类型(将Null识别为object)

[b]不能识别具体的对象类型(Function除外)

【实例】

console.log(typeof "jerry");//"string"

console.log(typeof 12);//"number"

console.log(typeof true);//"boolean"

console.log(typeof undefined);//"undefined"

console.log(typeof null);//"object"

console.log(typeof {name: "jerry"});//"object"

console.log(typeof function(){});//"function"

console.log(typeof []);//"object"

console.log(typeof new Date);//"object"

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

function Person(){};

console.log(typeof new Person);//"object"

2.Object.prototype.toString

【输出】[object 数据类型]的字符串形式

【功能】

[a]可以识别标准类型及内置对象类型

[b]不能识别自定义类型

【构造方法】

function type(obj){

return Object.prototype.toString.call(obj).slice(8,-1).toLowerCase();

}

【实例1】

console.log(Object.prototype.toString.call("jerry"));//[object String]

console.log(Object.prototype.toString.call(12));//[object Number]

console.log(Object.prototype.toString.call(true));//[object Boolean]

console.log(Object.prototype.toString.call(undefined));//[object Undefined]

console.log(Object.prototype.toString.call(null));//[object Null]

console.log(Object.prototype.toString.call({name: "jerry"}));//[object Object]

console.log(Object.prototype.toString.call(function(){}));//[object Function]

console.log(Object.prototype.toString.call([]));//[object Array]

console.log(Object.prototype.toString.call(new Date));//[object Date]

console.log(Object.prototype.toString.call(/d/));//[object RegExp]

function Person(){};

console.log(Object.prototype.toString.call(new Person));//[object Object]

【实例2】

function type(obj){

return Object.prototype.toString.call(obj).slice(8,-1).toLowerCase();

}

console.log(type("jerry"));//"string"

console.log(type(12));//"number"

console.log(type(true));//"boolean"

console.log(type(undefined));//"undefined"

console.log(type(null));//"null"

console.log(type({name: "jerry"}));//"object"

console.log(type(function(){}));//"function"

console.log(type([]));//"array"

console.log(type(new Date));//"date"

console.log(type(/d/));//"regexp"

function Person(){};

3.constructor

【输出】function 数据类型(){[native code]}或者function 自定义类型(){}

【功能】

[a]可以识别标准类型、内置对象类型及自定义类型

[b]不能识别undefined、null，会报错

【构造方法】

console.log(type(new Person));//"object"

function type(obj){

var temp = obj.constructor.toString();

return temp.replace(/^function (w+)().+$/,'$1');

}

【实例1】

console.log(("jerry").constructor);//function String(){[native code]}

console.log((12).constructor);//function Number(){[native code]}

console.log((true).constructor);//function Boolean(){[native code]}

//console.log((undefined).constructor);//报错

//console.log((null).constructor);//报错

console.log(({name: "jerry"}).constructor);//function Object(){[native code]}

console.log((function(){}).constructor);//function Function(){[native code]}

console.log(([]).constructor);//function Array(){[native code]}

console.log((new Date).constructor);//function Date(){[native code]}

console.log((/d/).constructor);//function RegExp(){[native code]}

function Person(){};

console.log((new Person).constructor);//function Person(){}

【实例2】

function type(obj){

var temp = obj.constructor.toString().toLowerCase();

return temp.replace(/^function (w+)().+$/,'$1');

}

console.log(type("jerry"));//"string"

console.log(type(12));//"number"

console.log(type(true));//"boolean"

//console.log(type(undefined));//错误

//console.log(type(null));//错误

console.log(type({name: "jerry"}));//"object"

console.log(type(function(){}));//"function"

console.log(type([]));//"array"

console.log(type(new Date));//"date"

console.log(type(/d/));//"regexp"

function Person(){};

console.log(type(new Person));//"person"

4.instanceof

【输出】true或false

【功能】

[a]可以识别内置对象类型、自定义类型及其父类型

[b]不能识别标准类型,会返回false

[c]不能识别undefined、null，会报错

【实例】

console.log("jerry" instanceof String);//false

console.log(12 instanceof Number);//false

console.log(true instanceof Boolean);//false

//console.log(undefined instanceof Undefined);//报错

//console.log(null instanceof Null);//报错

console.log({name: "jerry"} instanceof Object);//true

console.log(function(){} instanceof Function);//true

console.log([] instanceof Array);//true

console.log(new Date instanceof Date);//true

console.log(/d/ instanceof RegExp);//true

function Person(){};

console.log(new Person instanceof Person);//true

console.log(new Person instanceof Object);//true

以上内容就是详解JavaScript中的4种类型识别方法，希望大家喜欢。