JavaScript 数组清空，开始/末尾添加，删除元素

1、清空数组

array_1.splice(0,array_1.length)，两个参数，从前到后分别为：从数组索引为0的位置的元素开始，删除 array_1.length 个元素，结果 array_1 是方法执行后的值为 [] ，即array_1数组元素被清空了，array_2 则是执行函数后被删除的元素，因为array_1被全删除,故 array_2 接收的结果就是 array_1 被删除前的值

let array_1 = ["1","2","3","4"];
let array_2 = array_1.splice(0,array_1.length); 
//array_1 结果 []
//array_2 结果 ["0", "1", "2", "3", "4"]

2、在指定位置插入数组

array_1.splice(0,0,"0")，三个参数，从前到后分别为：从数组索引为0的位置的元素开始，删除0个元素，插入一个 "0" 元素，结果 array_1 是在起始位置新增了一个 “0” 元素，array_2 则是接收的 splice 函数执行后中删除的数组元素，本次未删除任何元素，故 array_2 返回为 []

let array_1 = ["1","2","3","4"];
let array_2 = array_1.splice(0,0,"0");
//array_1 结果 ["0", "1", "2", "3", "4"]
//array_2 结果 []

3、在数组末尾增/删元素

push() / pop() ，var_1接收的是函数执行后数组元素的个数，var_2 接收的是函数执行后被删除的元素

let array_1 = ["1","2","3","4"];
var var_1 = array_1.push("5");
//array_1 结果 ["1", "2", "3", "4", "5"]
//var_1    结果 5

var var_2 = array_1.pop();
//array_1 结果 ["1", "2", "3", "4"]
//var_1    结果 "4"

4、在数组首部增/删元素

unshift() / shift() - 在数组首部增/删元素，var_1接收的是函数执行后数组元素的个数，var_2 接收的是函数执行后被删除的元素

let array_1 = ["1","2","3","4"];
var var_1 = array_1.unshift("0");
//array_1  结果 ["0", "1", "2", "3", "4"]
//var_1     结果 5

var var_2 = array_1.shift();
//array_1  结果 ["1", "2", "3", "4"]
//var_1     结果 "0"

5、把一个（或多个）数组和（或）值与原数组拼接，返回拼接后的数组

concat()

let array_1 = ["1","2","3","4"];
let array_2 = ["7", "8"];
var var_1 = array_1.concat(array_2);
//array_1 结果 ["1", "2", "3", "4", "5", "6"]
// var_1  结果 ["1", "2", "3", "4", "5", "6"]

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array