//from()用于将 类数组结构转换为数组实例
//第一个参数是一个类数组对象，即任何可迭代的结构，或者有一个 length 属性 和可索引元素的结构

//不是数组的转化为数组
let arr = Array.from("Gaofeng");

console.log(arr); //["G", "a", "o", "f", "e", "n", "g"];

const m = new Map().set(1, 2);
const b = new Map().set(1, 2).set(3, 4);
console.log(m); //Map { 1 => 2 }
console.log(b); //Map { 1 => 2, 3 => 4 }
console.log(Array.from(b)); //[ [ 1, 2 ], [ 3, 4 ] ]
const c = new Set().add(1).add(2).add(3).add(4);
console.log(Array.from(c)); //[ 1, 2, 3, 4 ]

 Array.from()对现有数组执行浅复制

const a1 = [1, 2, 3, 4, {
          
    name: "gaofeng" }];
const a2 = Array.from(a1);
a1.push(5);
a1[4].name = "zhangsan";
console.log(a1); // [1, 2, 3, 4, { name: zhangsan }, 5 ]
console.log(a2); //[ 1, 2, 3, 4, { name: zhangsan } ]
console.log(a1 == a2);

const c1 = [1, 2, 3, 4];

const a4 = Array.from(c1, (x) => x ** 2);
console.log(a4); //[ 1, 4, 9, 16 ]

//
console.log(Array.of(1, 2, 3, 4)); //[ 1, 2, 3, 4 ]
//数组填充
const zeroes = [0, 0, 0, 0, 0];
zeroes.fill(7);
console.log(zeroes); //[ 7, 7, 7, 7, 7 ]
zeroes.fill(0);
console.log(zeroes); //[ 0, 0, 0, 0, 0 ]

//
zeroes.fill(6, 3);

console.log(zeroes); //[ 0, 0, 0, 6, 6 ]

/* let colors = ["red", "blue", "green"];
console.log(colors.toString());
console.log(colors.valueOf()); */

let colors = new Array();
let count = colors.unshift("red", "green"); // 从数组开头
console.log(colors);

/* let values = [1, 2, 3, 4, 5];
let sum = values.reduce((prev, cur, index, array) => prev + cur, 10);
console.log(sum); */

/* let values = [1, 2, 3, 4, 5];
let sum = values.reduce((prev, cur, index, array) => prev + cur, 10);
console.log(sum, values); */
let values = [{
          
    num: 0 }, {
          
    num: 1 }, {
          
    num: 2 }, {
          
    num: 3 }, {
          
    num: 4 }];
let sum = values.reduce(
  (prev, cur, index, array) => {
          
   
    console.log(prev, cur);
    return {
          
    num: prev.num + cur.num };
  },
  {
          
    num: 20 }
);
console.log(sum.num, values);

持续总结中…