数组操作
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对数组的最后一位进行操作
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添加
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书写格式：数组名.push(数据);
例：let arr = ["A","B","C"];
arr.push("D");
console.log(arr); //["A","B","C","D"]
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删除
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书写格式：数组名.pop();
例：let arr = ["A","B","C"];
arr.pop();
console.log(arr); //["A","B"]
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对数组第一位进行操作
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添加
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书写格式：数组名.unshift(数据);
例：let arr = ["A","B","C"];
arr.push(1);
console.log(arr); //[1,"A","B","C"]
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删除
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书写格式：数组名.shift();
例：let arr = ["A","B","C"];
arr.shift();
console.log(arr); //["B","C"]
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pushunshift 和 popshift 的区别
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添加是可以，一次性添加多个数据；
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删除每次只能删除一个；
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合并两个数组
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例： let arr = [1,2];
let arr1 = [3,4];
let arr2 = arr.concat(arr1);
let arr3 = [...arr,...arr1];
console.log(arr2); //[1,2,3,4]
console.log(arr3); //[1,2,3,4]
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截取 slice ()
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书写格式：数组名.slice(参数); //可以接收两个参数
例：
let arr = ["A","B","C","D","E","F"];
// 情况一：一个参数（截取的开始下标）；
截取的内容是包括开始下标及以后的所有数据；
let arr1 = arr.slice(2);
console.log(arr1); //["C","D","E","F"]
// 情况二：两个参数（截取的开始下标，截取的结束下标）；
截取的内容是开始下标（包括开始下标的内容） 到 结束下标（不包括结束下标的内容）的所有数据；
let arr2 = arr.slice(2,4);
console.log(arr2); //["C","D"]
// 情况三：当不存在输入值的内容，则返回空数组 即 [ ]
let arr3 = arr.slice(10);
console.log(arr3); //[ ]
// 情况四：当输入值为负值时，数组的长度加负值即下标，
则截取的内容是开始下标（包括开始下标的内容） 到 结束下标（不包括结束下标的内容）的所有数据；
let arr4 = arr.slice(-4,-2);
console.log(arr3); //["C","D"]
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splice() 会改变原数组
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书写格式：数组名.splice(参数); //可以接收三个参数
例：
let arr = ["A","B","C","D","E","F"];
//情况一： 两个参数
功能：剪切
第一个参数是起始下标，第二个为结束下标。（包含结束下标）
let arr1 = arr.splice(2,5);
console.log(arr1); //["C","D","E","F"]
console.log(arr); //["A","F"]
//情况二： 三个参数
功能：插入修改(取决于第二个参数；第二个值为 0 时，代表插入；第二个值为 1 时，代表修改)
let arr2 = arr.splice(1,0,5); //在下标为 1 的前面插入内容 5
console.log(arr2); //["A",5,"B","C","D","E","F"]
let arr3 = arr.splice(1,1,5); //将下标为 1 的数据改为内容 5
console.log(arr2); //["A",5,"C","D","E","F"]
//情况三： N个参数
从第三个参数开始，以后的内容都是要插入的值
let arr4 = arr.splice(1,0,5,6,7,8); //在下标为 1 的前面插入内容 5 6 7 8
console.log(arr4); //["A",5,6,7,8,"B","C","D","E","F"]
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一次性删除数组的内容
let arr = ["A","B","C","D","E","F"];
arr.length = 0;
console.log(arr); //[ ]
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数组转字符串 join()
let arr = [1,2,3];
let str = arr.join(",");
console.log(str,typeof str); //1,2,3 string
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字符串转数组
let str = "Say hello to everybody!";
let arr = str.split();
console.log(arr); //[
Say hello to everybody!]arr = str.split("");
console.log(arr); //[
S``a``y`` ``h``e``l``l``o`` ``t``o`` ``e``v``e``r``y``b``o``d``y``!]arr = str.split(" ");
console.log(arr); //['Say','hello','to','everybody!']
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遍历数组
let arr = ["A","B","C","D","E","F"];
//遍历输出数组中的每个值
for(let item of arr){
console.log(item);
}
//输出结果为 A B C D E F
//遍历输出数组中的每个值的下标
for(let item in arr){
console.log(item);
}
//输出结果为：0 1 2 3 4 5
//遍历输出数组中的每个值对应的键（下标）
for(let item of arr.keys()){
console.log(item);
}
//输出结果为：0 1 2 3 4 5
//遍历输出数组中的每个值
for(let item of arr.values()){
console.log(item);
}
//输出结果为 A B C D E F
//遍历输出数组中的每个值以及每个值对应的键（下标）
for(let item of arr.entries()){
console.log(item);
}
//输出结果为 [0,'A'] [1,'B'] [2,'C'] [3,'D'] [4,'E'] [5,'F']
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判断标识符是不是数组
let str = "123";
let arr = ["A","B","C"];
console.log(Array.isArray(str)); //false
console.log(Array.isArray(arr)); //true
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查找
let arr = ["A","B","C","D","C"];
//返回查找的值是否存在，存在则返回true,否则返回false
arr.includes("C"); //true
//从前往后找，找到第一个满足的值，返回其下标
arr.indexOf("C"); //2
//从后往前找，找到第一个满足的值，返回其下标
arr.lastIndexOf("C");//4
//如果没有找到，都会返回 -1
arr.indexOf("E");arr.lastIndexOf(); //-1
数组的使用
通过下标或索引号获取到具体值。
数组名[下标]
注：下标(索引)的起始值是0
例：
let arr = ["A","B","C","D"];
console.log(arr); //输出结果为 ["A","B","C","D"]
console.log(arr[0]); //输出结果为 A
console.log(arr[2]); //输出结果为 C
console.log(arr[10]); //输出结果为 undefined