Common Methods of JavaScript Arrays [Advanced] Contains 2 Example Questions

iterate over the array

PS: This article only explains the last three

1. while
2. for( ; ; )
3. for in
4. for of
5. map

let arr = ["a","b","c","d","e","f"];
for( var i in arr)//i是索引
for( var i of arr)//i是数组种具体的值
/*map的参数是一个回调函数，function的值作为map的参数*/
arr.map(function(value,index){
    
    
/*value是arr的值，index是数组的索引，记住参数顺序不能改变*/
})

Common methods for manipulating arrays

1. push
2. map
3. sort
4. filter
5. join

1:push
	let newArr= [];
	newArr.push("arr[i]");
--------------------------------------------
2:map/*map和filter的参数都是回调函数*/
/*从一个数组中筛选数据用arr.filter()*/
	arr.map(function(value,index){
    
    
})
--------------------------------------------
3:sort
	let arr = [1,3,2,6,5,4];
	arr.sort();//自动排序
--------------------------------------------
4:filter/*map和filter的参数都是回调函数*/
     let newArray = arr.filter(function(item) {
    
    
     	if (item > 3) {
    
    
        	return item;
            }
	})
--------------------------------------------
5:join
	//join    数组 拆分成 字符串
		let arr = [1,3,2,6,5,4];
        let str = arr.join(""); //1,3,2,6,5,4
        let str1 = arr.join(); //132654
        let str2 = arr.join("*"); //1*3*2*6*5*4
--------------------------------------------
6：string的split/*1-5方法都是 数组的方法   而本方法是字符的方法*/
	//split    字符串 分裂成 数组
	    let str = "apple"
        let str1 = str.split(); //['apple']
        let str2 = str.split(""); //['a', 'p', 'p', 'l', 'e']
        let str3 = str.split("+"); //['apple']  因为apple字符串里面没有+符号
        let str4 = str.split("l"); //['app', 'e']
        let str5 = str.split("p"); //['a', '', 'le']  因为有2个p,所以第2个p就变为''

example

Example 1: Find the index of the maximum value in an array

        let arr = [1, 3, 2, 4, 5, 6, 8, 9];
        let max = 0;
        let realindex = 0;
        arr.map(function(item, index) {
    
     //此处写filter和map函数都是一样的结果
            if (item > max) {
    
    
                max = item;
                realindex = index;
            }
        })
        console.log(realindex);
        console.log(max);

Example 2: Filter out all the information of the boys below and add them to a new array
let list = [
{name: "Xiao Ming",age: 8,sex: "Male"}, {
name: "Xiao Gang",age: 9, sex: "Male"},
{name: "Xiaohong",age:9,sex: "Female"}
]

method one

let newArr = list.filter(function(value, index) {
    
     //此处用filter和map得到的结果：分别有2个元素，3个元素（第3个为undefined）
            if (value.sex === "男") {
    
    
                return value;
            }
        })

Method Two

let newArr = [];
        for (let i = 0; i < list.length; i++) {
    
    
            if (list[i].sex === "男") {
    
    
                newArr.push(list[i]);
            }
        }

method three

let newArr = [];
        for (let i of list) {
    
    
            if (i.sex === "男") {
    
    
                newArr.push(i);
            }
        }