意想不到的console.log()输出题目

素颜马尾好姑娘i 2021-11-30 00:52 236阅读 0赞

### 一、 Number类型： ###

console.log(
        Number(true),            //1
        Number(false),           //0
    
        Number(undefined),        //NaN
        Number(null),             //0
        
        Number(''),              //0
        Number(' '),             //0
        
        Number('66'),            //66
        Number('066'),           //66
        Number('5e5'),          //500000
        Number('a'),            //NaN
        
        //对象...
        Number([]),            //0
        Number([3]),           //3
        Number(['']),         //0
        Number({}),           //NaN
        Number([1,2]),        //NaN
        Number(function () {})  //NaN
        
    );

### 二、 String类型和Boolean类型： ###

console.log(
    
        String(null),            //'null'
        String(2, [3]),           //2,3
        String({}),               //[object Object]
        String(function () {}),       //function () {}
    
        //Boolean类型
        Boolean(''),        //false
        Boolean(' '),        //true
        Boolean('1'),           //true
    
    );

### 三、隐式类型转数字类型： ###

console.log(
      //加法
       1 + null,         //1
       5 + '6',          //"56"
       5 + [],           //"5"
       1 + undefined,    //NaN
       3 + {},           //"3[object Object]"  
       2 + function() {},    //"2function(){}"
       [] + {}           //"[object Object]"
    
      //减
      'a' - 'b',            //NaN - NaN = NaN
       [] - 3,              // -3
       1 - undefined,       //NaN
       '5' * [],            //0
       null % true,         //0%1 = 0   
       "B" - "B" + 3,       //NaN - NaN + 3 = NaN
        
    );

### 四、比较类型： ###

console.log(
       null >= '',         //true        0 >= 0   
       'a' > 5,            //false        NaN
       { } > 2,            //false       NaN 
       undefined > false,    //false     NaN     
    
       //两边都是基本数据类型比较的时候，都会隐式转换为数字类型、
       15 == '15',         //true
       ' ' == false,       //true
       0 == '',            //true
       1 == true,          //true
       0 == false,         //true
       2 == false,         //false    2  0 
       'true' == true,     //false    'true' --> NaN    
    
        //undefined, null 与其它比较的时候，只有与它自己本身 以及 它俩相比较才会为true，其它的都是false
        undefined == undefined,        //true
        undefined == null,             //true
        null  ==  null,                //true
        undefined == 0,             //fasle
        undefined == '',            //false
        undefined == false,         //false             
        null == 0,                  //false
        null == '',                 //false
        null == false,              //false
     
    );

console.log(
        //对象转换为字符串的形式
    
        [2] == 2,            //true
        [] == 0,             //true
        [1] == true,         //true
        [1, 'b', 5] == '1,b,5'    //false
        ['a'] == ['a'],          //false
        [] == undefined,         //false
        [1, 'b', 5] == [1, 'b', 5] //false
        {a : 2} == 2,            //false 
        [null] == null,          //false
        {} == {},                //false
        [] == [],                //false
    );

//对象与对象相比，比较引用地址
    
    var fn1 = function() {
    
    }
    
    var fn2 = function() {
    
    }
    
    fn3 = fn1;
    console.log(fn1 == fn2);        //false  fn1和fn2函数的引用地址不同
    console.log(fn1 == fn3);        //true