JavaScript数组常用方法解析及数组扁平化

let user = ["zhangsan", "lisi"];
console.log(user.push("xiaoming")); //	3
console.log(user); // ["zhangsan", "lisi", "xiaoming"]
let user1 = ["xiaowang", "xiaoming"];
let user2 = ["zhangsan", "lisi"];
console.log(Array.prototype.push.apply(user1, user2)); // 	4
console.log(user1); // ["xiaowang", "xiaoming", "zhangsan", "lisi"]

let user = ["zhangsan", "lisi"];
console.log(user.pop()); //	lisi
console.log(user); //	["zhangsan"]
let empArray = [];
console.log(empArray.pop()); //	undefined

const user = ["zhangsan", "lisi", "xiaoming", "xiaowang"];
user.sort();
console.log(user); // ["lisi", "xiaoming", "xiaowang", "zhangsan"]
const array1 = [1, 30, 4, 21, 100000];
array1.sort();
console.log(array1); // [1, 100000, 21, 30, 4]


var numbers = [4, 2, 5, 1, 3];
let sortFun = function (a, b) {
  return a - b;
};
numbers.sort(sortFun);
console.log(numbers); // [1, 2, 3, 4, 5]

let user = ["zhangsan", "lisi"];
console.log(user.shift()); //	zhangsan
console.log(user); //	["lisi"]
let empArray = [];
console.log(empArray.shift()); //	undefined
let user1 = ["xiaoming", "xiaowang"];
console.log(user1.unshift("xiaoming1", "xiaowang1")); //	4
console.log(user1); //	["xiaoming1", "xiaowang1", "xiaoming", "xiaowang"]

let user = ["zhangsan", "lisi"];
let user1 = [["xiaowang"], { name: "xiaoming" }];
console.log(user.concat(user1)); // ["zhangsan","lisi",["xiaowang"],{name: "xiaoming"}]
console.log(user); // ["zhangsan", "lisi"]

let user = ["zhangsan", "lisi"];
console.log(user.indexOf("lisi")); // 1
console.log(user.indexOf("xiaoming")); // -1
let user1 = ["zhangsan", ["xiaowang"], { name: "xiaoming" }];
console.log(user1.includes("zhangsan")); // true
console.log(user1.includes(["xiaowang"])); // false
console.log(user1.includes({ name: "xiaoming" })); // false

let user = ["zhangsan", "lisi", "xiaoming"];
console.log(user.reverse()); // ["xiaoming", "lisi", "zhangsan"]
console.log(user); // ["xiaoming", "lisi", "zhangsan"]
let user1 = ["zhangsan", ["xiaowang", "lisi"], { name: "xiaoming" }];
console.log(user1.reverse()); // [{name: "xiaoming"},["xiaowang", "lisi"],"zhangsan"]

let user = ["zhangsan", "lisi", "xiaoming"];
console.log(user.join(" ")); // zhangsan lisi xiaoming
console.log(user.join("")); // zhangsanlisixiaoming
console.log(user.join(",")); // zhangsan,lisi,xiaoming
console.log(user.join({ a: 1 })); // zhangsan[object Object]lisi[object Object]xiaoming
console.log(user); // ["zhangsan", "lisi", "xiaoming"]

const animals = ["ant", "bison", "camel", "duck", "elephant"];
console.log(animals.slice(2)); // Array ["camel", "duck", "elephant"]
console.log(animals.slice(2, 4)); // Array ["camel", "duck"]
console.log(animals.slice(1, 5)); // Array ["bison", "camel", "duck", "elephant"]
console.log(animals.slice(-2)); // Array ["duck", "elephant"]
console.log(animals.slice(2, -1)); // Array ["camel", "duck"]
console.log(animals.slice()); // Array ["ant", "bison", "camel", "duck", "elephant"]

const months = ["Jan", "March", "April", "June"];
months.splice(1, 0, "Feb"); // 下表为1，插入一个元素
console.log(months); // ["Jan", "Feb", "March", "April", "June"]
months.splice(4, 1, "May"); // 替换下标为4的元素
console.log(months); // ["Jan", "Feb", "March", "April", "May"]
let del = months.splice(1, 1); // 删除
console.log(del); // ["Feb"]
console.log(months); // ["Jan", "April", "May"]

const isBelowThreshold = (currentValue) => currentValue < 40;
const array1 = [1, 30, 39, 29, 10, 13];
console.log(array1.every(isBelowThreshold)); // true

const array = [1, 2, 3, 4, 5];
const even = (element) => element % 2 === 0; //确认偶数
console.log(array.some(even)); // true;

let arr1 = [1, 2, [3, 4]];
console.log(arr1.flat()); // [1, 2, 3, 4]
let arr2 = [1, 2, [3, 4, [5, 6]]];
console.log(arr2.flat()); // [1, 2, 3, 4, [5, 6]]
let arr3 = [1, 2, [3, 4, [5, 6]]];
console.log(arr3.flat(2)); // [1, 2, 3, 4, 5, 6]
//使用 Infinity，可展开任意深度的嵌套数组
let arr4 = [1, 2, [3, 4, [5, 6, [7, 8, [9, 10]]]]];
console.log(arr4.flat(Infinity)); // [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
let objarray = [{ name: "zhangsan", children: ["张三"] }];
console.log(objArray.flat(Infinity)); // [{ name: "zhangsan", children: ["张三"] }]

const array1 = [1, 4, 9, 16];
const map1 = array1.map((x) => x * 2);
console.log(map1); // [2, 8, 18, 32]