JavaScript数组知识

javascript

浏览数:375

2019-1-8


JavaScript数组知识

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>数组操作</title>
    <link rel="icon" type="text/css" href="images/favicon.ico">
</head>
<body>

</body>
<script>
    /*
    //instanceof
    var arr = [12,23,45,6,89];
    console.log(arr instanceof Array);//true

    //Array.isArray(参数); // 判断参数是不是数组,返回布尔值;
    var arr = [1, 2, 3];
    var num = 123;
    console.log(Array.isArray(arr));//true
    console.log(Array.isArray(num));//false

    // 数组.toString() 把数组变成字符串,去除[] 内容有逗号链接
    var arr = ["aaa","bbb","ccc"];
    console.log(arr.toString());// aaa,bbb,ccc

    //数组.valueOf() 返回数组本身
    var arr = ["aaa","bbb","ccc"];
    console.log(arr.valueOf());//  ["aaa", "bbb", "ccc"]

    //数组.join(参数) 数组中的元素可以按照参数进行连接变成一个字符串
    var arr = ["aaa","bbb","ccc"];
    //console.log(arr.join("-"));//  "aaa-bbb-ccc"
    //console.log(arr.join(""));//     "aaabbbccc"
    //console.log(arr.join(" "));//   "aaa bbb ccc"

    //数组.push() //在数组的最末尾添加元素;
    var arr = [1,2,3,4];
    var arr1 = arr.push(0);
    console.log(arr);//[1, 2, 3, 4, 0]
    console.log(arr1);// 5 返回数组的长度

    //数组.pop() 不需要参数  在数组的最末尾删除一项
    var arr = [1,2,3,4];
    var arr2 = arr.pop();
    console.log(arr);// [1, 2, 3]  改变原数组
    console.log(arr2);// 4   返回值是被删除的一项

    //数组.unshift() //在数组的最前面添加一个元素;
    var arr = [1,2,3,4];
    var arr3 = arr.unshift(9);
    console.log(arr);//[9, 1, 2, 3, 4]
    console.log(arr3);//5 返回值是数组的长度

    //数组.shift() 不需要参数 在数组的最前面删除一项
    var arr = [1,2,3,4];
    var arr4 = arr.shift();
    console.log(arr);//[2, 3, 4] 返回被修改的数组
    console.log(arr4);// 1  返回被删除的一项

    //数组元素的排序
    //reverse() 翻转数组
    var arr = [12,56,89,98,68,87];
    var arr5 = arr.reverse();
    console.log(arr);// [87, 68, 98, 89, 56, 12]
    console.log(arr5);// [87, 68, 98, 89, 56, 12]

    //sort() // 数组中元素排序;(默认:从小到大)
    //默认:按照首个字符的Unicode编码排序;如果第一个相同那么就比较第二个...
    var arr = [12,35,24,56,42,8,5,68,86];
    var arr6 = arr.sort();
    console.log(arr);//[12, 24, 35, 42, 5, 56, 68, 8, 86]
    console.log(arr6);//[12, 24, 35, 42, 5, 56, 68, 8, 86]

    //sort() 用回调函数进行升序和降序的排列
    var arr = [12,35,24,56,42,8,5,68,86];
    arr.sort(function(a,b){
        return a-b;//升序排列
    });
    console.log(arr);//[5, 8, 12, 24, 35, 42, 56, 68, 86]

    //数组元素的操作
    //concat()
    var arr = [1,2,3];
    var arr8 = ["a","b","c"];
    var arr9 = arr.concat(arr8);
    console.log(arr);//[1, 2, 3]
    console.log(arr8);//["a", "b", "c"]
    console.log(arr9); //[1, 2, 3, "a", "b", "c"]

    //数组.slice(开始索引值,结束索引值);不包括结束索引 //数组截取;
    var arr = [1, 2, 3, "a", "b", "c"];
    var arr10 = arr.slice(1,4);
    console.log(arr);//[1, 2, 3, "a", "b", "c"]
    console.log(arr10);//[2, 3, "a"]

    //数组.splice(开始索引值,删除几个,替换内容1,替换内容2,...);
    // 替换和删除; 改变原数组;返回值是被删除/替换的内容
    var arr = [1,2,3,4,5,6,'a','b','c','d','e','f'];
    //var arr11 = arr.splice(5);//从索引为5开始截取到最后
    //console.log(arr);//[1, 2, 3, 4, 5]
    //console.log(arr11);//[6, "a", "b", "c", "d", "e", "f"]

    //var arr12 = arr.splice(2,5);//从索引为2开始截取5个元素
    //console.log(arr);//[1, 2, "b", "c", "d", "e", "f"]

    arr.splice(6,3,"aaa","bbb","ccc");//删除并替换
    console.log(arr);// [1, 2, 3, 4, 5, 6, "aaa", "bbb", "ccc", "d", "e", "f"]

    //数组.indexOf(元素); // 给元素,查索引(从前往后)
    // 数组.lastIndexOf(元素); // 给元素,查索引(从后往前)
    var arr = ["a","b","c","d","e","f"];
    console.log(arr.indexOf("e"));// 4
    console.log(arr.lastIndexOf("c"));//2
    */

    //数组迭代(遍历)
    /*数组.every() 对数组中每一项运行回调函数,如果都返回true,every返回true,如果有一项返回false,
    则停止遍历 every返回false;不写默认返回false*/
    /*var arr = [1,2,3,4,5];
    arr.every(function(ele,index,arr){
        console.log(a);//元素
        console.log(b);//索引
        console.log(c);//数组本身
    });*/

    /*var arr = [123,234,567,768,987];
    //every返回一个bool值,全部是true才是true;有一个是false,结果就是false
    var bool = arr.every(function(ele,index,arr){
        if(ele>100){
            return true;
        }else{
            return false;
        }
    });
    console.log(bool);*/

    /*filter()对数组中每一项运行回调函数,该函数返回结果是true的项组成的新数组
    新数组是有老数组中的元素组成的,return为ture的项;*/
    /*var arr = [123,123,45,678,54,678];
    var arr0 = arr.filter(function(element,index,array){
        if(element>100){
            return true;
        }else{
            return false;
        }
    });
    console.log(arr0);//[123, 123, 678, 678]*/

    //forEach() 和 for循环一样没有返回值
    /*var arr = [1,2,3,4,5,6,7];
    arr.forEach(function(element,index,array){
        console.log(element);
        console.log(index);
        console.log(array);
    });*/

    /*map()对数组中每一项运行回调函数,返回该函数的结果组成的新数组。
    return什么新数组中就有什么,不return返回undefined,对数组二次加工。*/
    /*var arr = [1,2,3,4,5,6,7,8];
    var newArr = arr.map(function(element,index,array){
        if(index==2||index==3){
            return element;
        }else{
            return element*2;
        }
    });
    console.log(newArr);// [2, 4, 3, 4, 10, 12, 14, 16]*/

    //some()对数组中每一项运行回调函数,如果该函数对某一项返回true,则some返回true; 像杀手,有一个成功,就胜利了!!!
    /*var arr = [1,2,4,5,6,7,8,10];
    var bool = arr.some(function(ele,index,array){
        if(ele%3==0){
            return true;
        }
        return false;
    });
    console.log(bool);*/

    //数组的清空
    /*1、arr.length = 0; 伪数组无法清空
    * 2、arr.splice(0);  伪数组中没有该方法
    * 3、arr = []; 可以操作伪数组(推荐)
    * 4、伪数组:就是长的像数组,但是没有数组的方法;也不能添加和删除元素;
    *
    * */
    //清空数组的案例
    /*function test(){
        //arguments.length = 0;//console.log(arguments);打印Arguments [0: 1, 1: 2, 2: 3, 3: 4, callee: ƒ, Symbol(Symbol.iterator): ƒ]
        //arguments.splice(0);//console.log(arguments);//Uncaught TypeError: arguments.splice is not a function
        arguments = [];//可以清空 返回空数组
        console.log(arguments);
    }
    test(1,2,3,4);*/

    //数组案例
    /*
    * ["刘备","张飞","关羽"] 1.将一个字符串数组输出为|分割的形式,比如“刘备|张飞|关羽”。使用两种方式实现
    * */
    //方法一
    /*var arr = ["刘备","张飞","关羽"];
    var arr1 = arr.join('|');
    console.log(arr1);//"刘备|张飞|关羽"*/

    //方法二
   /* var arr = ["刘备","张飞","关羽"];
    var separator = "|";
    var str = arr[0];
    for(var i = 1;i<arr.length;i++){
        str += separator+arr[i];
    }
    console.log(str);//"刘备|张飞|关羽"*/   //["c", "a", "z", "a", "x", "a"] 输出a所在的索引
    /*var arr = ["c", "a", "z", "a", "x", "a"];
    arr.forEach(function(element,index,array){
       if(element=="a"){
           console.log(index);//1,3,5
       }
    });*/

    /*判断特殊情况
        false == ""  // true
        false == []  // true
        false == {}  // false
        "" == 0      // true
        "" == []     // true
        "" == {}     // false
        0 == []      // true
        0 == {}      // false
        0 == null    // false
        null == undefined // true
        []==false // true
        [] == ![] // true 
        */

    /*var a = "0";
    console.log(Boolean(a));//true
    var b = false;
    console.log(Boolean(b));//false

    console.log(a==b);//true     == 比较的是强制类型转换后的值     === 是直接比较
    */
   

   // 数组.toString() 把数组变成字符串,去除[] 内容有逗号链接
   //let arr = [1,2,3,4,5,6,7,8,9];
   //console.log(arr.toString()); // '1,2,3,4,5,6,7,8,9'   //数组.valueOf() 返回数组本身
   //let arr = [1,2,3,4,5,6,7,8,9];
   //console.log(arr.valueOf());//[1, 2, 3, 4, 5, 6, 7, 8, 9]

   //数组.join(参数) 数组中的元素可以按照参数进行连接变成一个字符串
   // var arr = ["aaa","bbb","ccc"];
   // console.log(arr.join("-"));//  'aaa-bbb-ccc'
   // console.log(arr.join(""));//     'aaabbbccc'
   // console.log(arr.join(" "));//   'aaa bbb ccc'
   // console.log(arr.join("~"));//  'aaa~bbb~ccc'
   
   
    //sort() 用回调函数进行升序和降序的排列 箭头函数
    //var arr = [12,35,24,56,42,8,5,68,86];
    //升序
    //arr.sort((a,b) => a-b);
    //console.log(arr);//[5, 8, 12, 24, 35, 42, 56, 68, 86]
    
    //降序
    //arr.sort((a,b) => b-a);
    //console.log(arr);
   
  
   
</script>
</html>