数组

标签（空格分隔）： 排序sort

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创建数组：
var arr=new Array(3,true,"gd","good");
var arr=["hello",33,55,true]

var arr = ["bob", "James", "Jet li", 45, "juli"];
    console.log(arr.length);//5
    console.log(arr.indexOf("Jet li"));//2
    console.log(arr.slice(2,4));//取头不取尾  "Jet li", 45
    console.log(arr.pop()); //juli  
    console.log(arr.length);//4
    console.log(arr.push("Jack"));
    console.log(arr);//["bob", "James", "Jet li", 45, "Jack"]
    console.log(arr.unshift("angel",33));//从数组开始插入元素
    console.log(arr); //"angel", 33, "bob", "James", "Jet li", 45, "Jack" 
    console.log(arr.shift())//弹出第一个元素
    console.log(arr);//[33, "bob", "James", "Jet li", 45, "Jack"]
    console.log(arr.splice(2,3,"red", "blue"));//返回删除的元素  ["James", "Jet li", 45]
    console.log(arr);//[33, "bob", "red", "blue", "Jack"]
    console.log(arr.join("|")); //33|bob|red|blue|Jack
    console.log(arr.sort());//排序
    console.log(arr.reverse());//反向排序
    //concat 连接两个字符数组
    console.log(arr.concat("hello","world"));//["red", "bob", "blue", "Jack", 33, "hello", "world"]
    console.log(arr);//["red", "bob", "blue", "Jack", 33]

map函数

        var arr = [2, 9, 3, 0, 2];
        function f(x){
            return x*x;
        }
        console.log(arr.map(f));//[4, 81, 9, 0, 4]
        console.log(arr.map(String));//["2", "9", "3", "0", "2"]

reduce 函数

       var arr = [2, 9, 3, 4, 2];//求和
        function f(x,y){
            return x+y;
        }
        console.log(arr.reduce(f));//20

        var arr = [2, 9, 3, 4, 2];//求积
        function f(x,y){
            return x*y;
        }
        console.log(arr.reduce(f));//432

       var arr = [2, 9, 3, 0, 2];输出29302
        function f(x,y){
            return x*10+y;
        }
        console.log(arr.reduce(f));//29302

排序 sort
默认排序是按照，字符串排序，ASCII码排序；
sort()方法会直接对Array进行修改，它返回的结果仍是当前Array

        var arr = [2,4,99,33,9,20];
        console.log(arr.sort());//[2, 20, 33, 4, 9, 99]
        

从大到小排序

    var arr = [2,4,99,33,9,20];
        
        function f(x,y) {
            if(x<y){
                return 1;
            }
            if{
                return -1;
            }
            return 0;
        }
        console.log(arr.sort(f));//[99, 33, 20, 9, 4, 2]

从大到小排序

    var arr = [2,4,99,33,9,20];
        
        function f(x,y) {
            if(x<y){
                return -1;
            }
            if{
                return 1;
            }
            return 0;
        }
        console.log(arr.sort(f));//[2, 4, 9, 20, 33, 99]