对象常用方法

var str = "llinihao mezaigama";
var str2 = str.charCodeAt(5);//位置5的字符是h，h的Unicode编码是104
var str3 = str.charCodeAt(3);
console.log(str3); // 110
console.log(str2); // 104

var str1 = "lixiaoqi";
var str2 = ‘zaijian‘;
console.log(str2.concat(str1));//把str1连接到str2上
// 结果 lixiaoqizaijian

var str1 = "lixiaoqi";
var num1 = str1.indexOf(‘o‘); //检索字符串，返回的是字符在字符串的下标
//字符串的下标是从0开始计数
var num2 = str1.indexOf(‘lllll‘); //没有找到匹配的值，返回-1
var num3 = str1.indexOf(‘ni‘); //没有找到匹配的值，返回-1
console.log(num1); // 5
console.log(num2); // -1
console.log(num3); // -1

var str1 = "lixiaoqi";
var str2 = str1.match(‘iao‘); //检索字符串，返回的是字符
var str3 = str1.match(‘lll‘);//没有指定的字符，返回的是null
console.log(str2);
console.log(str3);

var str1 = "nihaome";
var str2 = "lixiaoqi";
var str3 = str1.replace(str1.match(‘hao‘),str2.match(‘lixi‘));
//找到str1的hao，找到str2的lixi，用str2替换掉str1
console.log(str3);

ar str1 = "lixiaoqi nihaoya zaiganma";
var str2 = "nihaoya";
var str3 = "wobuzai";
var num1 = str1.search(str2);//返回的是第一个字符所在的位置
var num2 = str1.search(str3); //未检测到返回-1
console.log(num1);
console.log(num2);

var str1 = ‘nihaoya wobuhaoya‘
console.log(str1.slice(4,9)); //4位置开始，到9的前一个位置结束
console.log(str1.slice(2,14));//start位置开始，end前一个位置结束
console.log(str1);//原字符串不变
console.log(str1.slice(-1,0)); //返回的是空字符串
console.log(str1.slice(30,100)); //长度超过字符串的长度，返回空字符串
console.log(str1.slice(-1,10));//返回的是空字符串

var str1 = "nihao-zaijian-dajiahao";
console.log(str1.split(‘‘));
var str2 = str1.split(‘-‘);
console.log(str2);
console.log(str1);//原字符串不变

var str = "NIHAOME WOHENHAOnizaiganmane";
console.log(str.toLocaleLowerCase());
var str1 = str.toLocaleLowerCase();
console.log(‘-----------‘);
console.log(str1);
console.log(str);//原字符串不变

var str = "deawwWWEzaiganmane";
console.log(str.toLocaleUpperCase());
var str1 = str.toLocaleUpperCase();
console.log(‘-----------‘);
console.log(str1);
console.log(str);//原字符串不变

var str = "deawwWWEzaiganmane";
console.log(str.toLowerCase());
var str1 = str.toLowerCase();
console.log(‘-----------‘);
console.log(str1);
console.log(str);//原字符串不变

var str = "deawwWWEzaiganmane";
console.log(str.toUpperCase());
var str1 = str.toUpperCase();
console.log(‘-----------‘);
console.log(str1);
console.log(str);//原字符串不变

var str = "nihaoya wohenhao dajiahao"
var str3 = str.substr(3,19);//字符串中空格不占位置，从3开始，到19结束
console.log(str3);

var str = "nihaoya wohenhao dajiahao"
var str3 = str.substring(3,19);//字符串中空格占位置，从3开始，到18结束
var str4 = str.substr(3,19);//空格不占位。从3开始到19结束
console.log(str4);
console.log(‘-------------‘);
console.log(str3);

 var obj = { a: 1 };
 var copy = Object.assign({}, obj);
 console.log(copy);        // { a: 1 }

.当键值为正常字符时，返回的键的值为字符串
    var obj1 = {a:1,b:2};
    var obj2 = Object.entries(obj1);
    console.log(obj2) ;      //  [ ["a":1],["b":2] ] 
 
（2）.当键值为数字时，返回的键的值也是字符串
    var obj = { 0: ‘a‘, 1: ‘b‘, 2: ‘c‘ };
    console.log(Object.entries(obj));     // [ [‘0‘, ‘a‘], [‘1‘, ‘b‘], [‘2‘, ‘c‘] ] 
 
（3）.当键值的数字错乱无序时，它会将其排序后返回
   var anObj = { 100: ‘a‘, 2: ‘b‘, 9: ‘c‘ };
   console.log(Object.entries(anObj));   //[["2","b"],["9","c"],["100","a"]] 

(1).比较字符串(单纯的比较字符串的每一位，如果完全相同返回true,只要有一个不一样，返回false)
Object.is(‘foo‘, ‘foo’);          //true;  
 
Object.is(‘fo‘, ‘foo’);           //false
 
(2).比较数组 (对数组无感，即使是相同的数组，或者是相同的空数组，都返回false)
Object.is([11,12],[11,12]).        //false
 
Object.is([],[])                   //false 
 
(3).比较window
Object.is(window, window)           //true
 
Object.is(window, document);       //false
 

(4).比较特殊对象undifined 和null(undefined和null都等于它本身，但undefined不等于null)
Object.is(null, null);                      //true

Object.is(undefined,undefined);            //true
 
Object.is(undefined,null);                 //false 
 
(5)比较正常对象()
复制代码
var test={a:1,b:2};     

var test1={a:2,b:5};
 
Object.is(test,test1)            //false
----------------------------------------------------------
var test={a:1,b:2};              //比较的两端需为一样的元素，当一边为变量时，另一边也必须是变量
 
Object.is(test,{a:1,b:2}).       //false
 
Object.is(test,test).            //true。