js中的typeof和instanceof和===

Posted 2020-10-05 lonecloud

typeof：

　　用于判断number/string/boolean/underfined类型/function

　　不能判断：null和object ，不能区分object和Array

instanceof：

　　判断具体的对象类型

===：

　　用于判断undefined和null

 

 

 

 

 

    //五种基本类型
    var num=1;
    var str="abc";
    var bl=true;
    var nu=null;
    var undef=undefined;
    //三种特殊类型
    var obj=new Object();
    var arr2=["1",2,true];
    var fun=function () {
        
    }
    write("-------typeof-----------")
    write(num,typeof num);//1 number
    write(str,typeof str);//abc string
    write(bl,typeof bl);//true boolean
    write(nu,typeof nu);//null object
    write(undef,typeof undef)//undefined undefined
    write(obj,typeof obj);//[object Object] object
    write(arr2,typeof arr2);//1,2,true object
    write("-----------===-----------")
    write(num,typeof num==="number");//1 true
    write(str,typeof str==="string");//abc true
    write(bl,typeof bl==="boolean");//true true
    write(nu,typeof nu==="object");//null true
    write(undef,typeof undef==="undefined")//undefined true
    write(obj,typeof obj==="object");//[object Object] true
    write(arr2,typeof arr2==="object");//1,2,true true
    write(fun,typeof fun==="function");//function () { } true
    write("---------instanceof---------------")
    write(obj,obj instanceof Object)//[object Object] true
    write(arr2,arr2 instanceof Array);//1,2,true true
    write(arr2,arr2 instanceof Object);//1,2,true true
    write(fun, fun instanceof Function)//function () { } true
    write(fun, fun instanceof Object)//function () { } true