03JavaScript程序设计修炼之道 2019-06-02_15-20-09 for each 数组es6的方法

你的名字 2021-12-11 04:37 182阅读 0赞

25array4.html

<!DOCTYPE html>
    <html lang="en">
    <head>
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        <meta http-equiv="X-UA-Compatible" content="ie=edge">
        <title>Document</title>
    </head>
    <body>
        <script>
            // forEach()
            var arr = [11,3,56,56,34,100,9,100];
            /*
            arr.forEach(function(item,index) {
                console.log(index+"-"+item);
            });
            */
            arr.forEach((item,index)=>{
                //console.log(index+"-"+item);
                if(item%2===0) {
                    console.log(item);
                }
            });
            // 求上述数组最大值
            var max = arr[0];
            arr.forEach((item)=>{
                if(item>max) {
                    max = item;
                }
            });
            console.log(max);
    
            // indexOf() 查找元素在数组中第一次出现的索引 假如不存在返回值-1
            var index = arr.indexOf(200);
            var index2 = arr.lastIndexOf(100); //从右往左找
            console.log(index);//4
            console.log(index2); // 6
            // 对数组进行去重
            function noRepeat(arr) {
                var newArr = [];
                // 对arr循环 每一次拿到元素 判断是否在newArr中 没有就加到newArr 
                arr.forEach((item)=>{
                    if(newArr.indexOf(item) === -1) {
                        newArr.push(item);
                    }
                });
                return newArr;
            }
            console.log(noRepeat(arr));
    
            // map filter reduce some every 不会改变原数组
            var array = [12,14,5,6,32,10];
            /*var newArr = array.map((item)=>{
                return item*1.2;
            });
            // filter过滤 由函数返回值为true的元素所组成
            var newArr = array.filter((item)=>{
                return item>12;
            });
            */
            // reduce 收敛
            /*
                第一次 prev 12  next 14  
                第二次 prev undefined next 5
                第三次 prev undefined next 6
                ...   
    
                从第二次开始的prev 是上一次的函数返回值   
            */
            var sum = array.reduce((prev,next)=>{
                console.log(prev+"---"+next);
                return prev+next;
            });
            // 当reduce传入第二个参数 第一次的prev指向第二个参数
            var sum2 = array.reduce((prev,next)=>{
                console.log(prev+"---"+next);
                return prev+next;
            },6);
            console.log(sum2);
            //console.log(newArr,array);
            // some 返回true/false 
            var arr2 = [10,4,5,6,11,20]; // 
            var res = arr2.some((item)=>{
                console.log(item);
                return item>100;
            });
            console.log(res); // true
            console.log("--------------");
            // every 直到第一个为false停止循环 否则返回true
            var res2 = arr2.every((item)=>{
                console.log(item);
                return item>10;
            });
            console.log(res2); 
        </script>
    </body>
    </html>

26array5.html

<!DOCTYPE html>
    <html lang="en">
    <head>
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        <meta http-equiv="X-UA-Compatible" content="ie=edge">
        <title>Document</title>
    </head>
    <body>
        <script>
            // Math.pow()
            // es6新增的 from 把数组或类数组变成数组 会复制一份
            var arr = [1,2,3];
            var newArr = Array.from(arr);
            console.log(newArr);
            // 类数组 并不是真正的数组 而是对象 arguments
            function fn() {
                //arguments.push(10); 报错
                var arguments = Array.from(arguments);
                arguments.push(12);
                console.log(arguments instanceof Array);
            }
            fn(1,2,3);
            //console.log(arr instanceof Array);
            var obj = {
                "0": 10,
                "1":20,
                length: 2
            }
            var arr2 = Array.from(obj);
            console.log(arr2);
            // of fill copyWithin
            var array = new Array(3); //  var array = [3];
            var array1 = new Array(3,4); 
            var array2 = Array.of(3,4);// 3是元素
            console.log(array,array.length);
            console.log(array1,array1.length);
            console.log(array2,array2.length);
            // fill copyWithin
            var res = [1,2,3,4].fill(5,1,3); // [1,5,5,4]
            var res2 = [1,2,3,4].copyWithin(1,0,2); // 用序号为0的元素一直到序号为2但不包含2的元素 1 2
            console.log(res);
            console.log(res2);// [1,1,2,4]
            // es7 includes 
            console.log([10,12,23,43].includes(100));// false 不存在 true存在
            // find findIndex （keys values）
            var find = [1,2,3,4,5,3].find((item,index,arr)=>{
                console.log("fn");
                return item==13;
            });
            var findIndex = [1,2,3,4,5,3].findIndex((item,index,arr)=>{
                return item==3;
            });
            console.log(findIndex);
        </script>
    </body>
    </html>

27array6.html

<!DOCTYPE html>
    <html lang="en">
    <head>
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        <meta http-equiv="X-UA-Compatible" content="ie=edge">
        <title>Document</title>
    </head>
    <body>
        <script>
            // 解构赋值 解析数组或对象的结构为不同的变量提取值
            //var name = "along";
            //var age = 32;
            var [name,age]  = ["along",32];
            console.log(name);
            console.log(age);
            //var [x,y,z]   = [1,[2.2,2.3]];
            //var [x,[y,z]]   = [1,[2.2,2.3]];
            //console.log(x,y,z); // 1 [2.2,2.3] undefined
            var [json,arr,num] = [{a:10,b:20},[1,2,3],10];
    
            var [,,x=4]  = [1,2];
            console.log(x);
            var [x,...y] = [10,20,30,40];// 剩余项
            console.log(x,y);// 10 [20,30,40]
    
            var arr = [1,2,3];
            var [...arr1] = arr; // 克隆数组
            console.log(arr1);
    
            var x  = 10, y = 20;
            /*
            var temp = x;
            x = y;
            y = temp;
            */
            [x,y] = [y,x];
            console.log(x,y);
         </script>
    </body>
    </html>

转载于:https://www.cnblogs.com/HiJackykun/p/11135520.html