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

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】

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。