JavaScript测试数据类型的三种方法

# typeof

console.log(typeof a);    //undefined

 

console.log(typeof(true));  //boolean

 

console.log(typeof '111');  //string

 

console.log(typeof 111);   //number

 

console.log(typeof nan);   //number

 

console.log(typeof null);  //object

 

var str = new string();

console.log(typeof(str));    //object

 

var  fn = function(){};

console.log(typeof(fn));  //function

 

class box{

　　constructor（）{

　  　

　　}

}

var box = new box（）；

console.log(typeof box);  //object

# object.prototype.tostring.call();

 

console.log(object.prototype.tostring.call("aaa"));　　//[object string]

 

console.log(object.prototype.tostring.call(111));　　//[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: "zhang"}));　　//[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(/a/));　　//[object regexp]

class test{

　　constructor(){

　　}

}

var test = new test();

console.log(object.prototype.tostring.call(test));　　//[object object]

 

# constructor

 

console.log((111).constructor.name) 　　//number

console.log(("111").constructor.name) 　　 //string

console.log((aaa).constructor.name)　　 //aaa is not defined

console.log((/a/).constructor.name)　　 //regexp

console.log((true).constructor.name)　　 //boolean

console.log(({name:"zhang"}).constructor.name)　　 //object

console.log((new date).constructor.name)　　 //date

console.log(([]).constructor.name) 　　//array

console.log((function(){}).constructor.name) 　　//function

class box{

　　constructor(){

　　}

}

var test = new box();

console.log(test.constructor.name)　　 //box