Front-end basics - arrays and common methods (push shift join toString pop unshift sort concat slice splice indexOf ever), loop (9)

array

create

           let arry1=new Array();
            let arry2=new Array(10);
            let Array3=new Array("fff","fbbb","mooo");
            let array4=["bv","mn","op"];
            let array5=[0,2,9,10,20,8];

Usual way push shift join toString pop unshift sort concat slice splice indexOf every some filter

            let arry5=[0,1,2,3];
            let atty6=arry5.push(8,9,10)//将数组添加到末尾
            console.log(arry5);

            let item=arry5.shift();//移除第一项并返回该项
            console.log(item);
            if(Array.isArray(arry1)){};//判断是否为数组
            console.log(Array3.join('_'));//设置连接符
            console.log(Array3.toString());//数组转字符串
            console.log(Array3.pop());//移除数组末尾最后一项并返该项

            console.log(Array3.unshift("000","sdbasb"))//在数组的前端添加任一一项并返回数组长度
       
            console.log(Array3);
            console.log(Array3.sort());//首先将数组里面的值转成字符串。然后比较字符串的编码的大小
            function compare(values1,values2)
            {

              return values1-values2;
            }
            array5.sort(compare);//按照函数比较结果排序
            console.log(array5);
            //concat
            console.log(Array3.concat(array4));

            ///slice
            console.log(array5.slice(1));
            console.log(array5.slice(1,3));
           // console.log(array5.slice(-1,-3));//负数加上数组长度，等同于array5.slice(5,3)

            //splice 获取到截取是我内容 将截取内容从原数组删除
            let arraysplice=["00","11","22","330","44"];
            console.log(arraysplice.splice(0,2));//截取从0到2的项并移除
            console.log(arraysplice);
            //插入
           let remove= arraysplice.splice(0,1,"dfd","gfnfdn")
            console.log(remove);
            console.log(arraysplice);
            //代替
            let remove0= arraysplice.splice(1,1,"...","```")
            console.log(arraysplice);





            //indexof(item)从头往后查找该项索引
            let array5indexof=[0,2,3,9,10,20,8];
            console.log(array5indexof.indexOf(3));//从0开始查找3
            console.log(array5indexof.indexOf(3,2));//从2开始查找3

            console.log(array5indexof.lastIndexOf(3));//从末尾开始查找3
            console.log(array5indexof.lastIndexOf(3,2));//从2开始查找3

           // every some filter
           let array5i =[0,2,3,9,10,20,8];
           let res1=array5i.every(function(item,index)
           {
               return item>8;
           })
           console.log(res1);
           let res2=array5i.some(function(item,index)
           {
               return item>8;
           })
           console.log(res2);
           //过滤
           let res3=array5i.filter(function(item,index)
           {
               return item>8;
           })
           console.log(res3);

cycle

for in 、for of、forEach、reduce

    <script>
            let  obj={
      
      
                name:"jimgreem",
                age:55,
            };
      // for in 循环只能获得对象的键名 不能获得键值   for of 循环允许遍历获取键值
            for(let key in obj)
            {
      
      
              console.log(key);//name age
            }

            for(let key of Object.keys(obj))
            {
      
      
              console.log(key);
            }
             let arr=["red","ggg","blue"];
           for (let item of arr) 
           {
      
      
             console.log(item);
           }
            let arry=[3,20,51,23,10,88,3];
            for (let i=0;i<arry.length;i++)
            {
      
      
               console.log(i);
            }
          //forEach无法使用return break continue  但是 for in与for of可以
            arr.forEach(element => {
      
      
                 
                console.log(element);
            });
            //reduce方法  
            var sum=arry.reduce(function(pre,cur){
      
      //pre 的初始值为0，cur为3，完了后下一次的prev为3 cur为9
                return pre+cur;//求数组之和
            },0);
           console.log(sum);
            var max=arry.reduce(function(pre,cur){
      
      
                return Math.max(pre,cur);//求最大值
            });
            console.log(max);
        </script>