1.循环遍历对象

1.1vue 在html里面循环遍历对象

v-for=" (val, key , i) in dimItemMap" :key="key"
val-每一项
key -key值
i-第几个

<el-table-column prop="score" label="评分":show-overflow-tooltip="true" align="center"><template slot-scope="scope"><span><span v-for=" (val, key , i) in scope.row.dimItemMap":key="key">{{val.score}}//score为键，val.score为值</span></span></template></el-table-column>

1.2 在js里面forin遍历对象

for…in 循环主要是为了遍历对象而生，不适用于遍历数组

let data=[{wiun2dvi:232,wiun3dvi:55,wiu4ndvi:33,wiun1dvi:24432}];
    data.forEach((item,index)=>{for(const keyin item){
        console.log("item[key]",item[key]);//值
        console.log("key",key);//键}})

2.循环遍历数组

2.1 vue 在html里面循环遍历数组

<el-table-column v-for="item in tableCol":key="item.id":prop="item.id":label="item.name":show-overflow-tooltip="true" align="center"><template slot-scope="scope"><span>{{scope.row.dimItemMap?scope.row.dimItemMap[item.id].name:""}}</span></template></el-table-column>

<el-table-column prop="score" label="评分":show-overflow-tooltip="true" align="center"><template slot-scope="scope"><span><span v-for=" (item, index) in scope.row.dimItemMap":key="index">{{item.score}}</span></span></template></el-table-column>

2.2 在js里面for遍历数组

let id=1524466for(let i=0; i< list.length; i++){let a= list[i];if(a.id=== id){return a.name;}}

2.3 在js里面forof遍历数组

let arr=[{name:12,hello:"wsdfnioq",},{name:12,hello:"wsdfnioq",},{name:12,hello:"wsdfnioq",}]for(const iof arr){
                console.log("i", i);}//i {name: 12, hello: 'wsdfnioq'}// i {name: 12, hello: 'wsdfnioq'}//i {name: 12, hello: 'wsdfnioq'}

let arr=[['name',"张三"],['地址','北京'],['手机','123']]for(const[value0, value1]of arr){
    console.log('k', value0, value1);}// k name 张三// k 地址 北京// k 手机 123

2.4 forin，不推荐对数组进行遍历

let arr=["lsadnkol","klsmvaod","lpsaojfoas"]for(const keyin arr){
    console.log("arr", key,typeof key, arr[key]);}// 0 string lsadnkol// 1 string klsmvaod// 2 string lpsaojfoas

2.4 forEach() 函数遍历数组

①无任何返回，可改变原来数组中的内容
②循环次数：数组的长度
③不支持return，不需要return语句

如下案例：给每个对象中添加age属性

let forArr=[{name:'tom',sex:'man'},{name:'linda',sex:'woman'},]
     forArr.forEach((item,index)=>{
        console.log("forEach循环==index==",index,item);
         item.age=27})

    console.log("forArr==遍历后===",forArr)// forArr ---->[{name:'tom',sex:'man',age:27},{name:'linda',sex:'woman',age:27}]

3.循环遍历字符串

3.1for

let s="abcd"for(let i=0; i< s.length; i++){
      console.log(i,typeof i, s[i]);//i为索引,s[i]为值,typeof i 为number}//  0 number a//  1 number b//  2 number c//  3 number d

3.2 forin

let s="abcd"for(const keyin s){
    console.log("key", key,typeof key, s[key]);//key为索引,s[key]为值,typeof key 为string}// 0 string a// 1 string b// 2 string c// 3 string d

3.3 forof

let s="abcd"for(const iof s){
    console.log("i", i);//i为值}// a// b// c// d