for..of会遍历可迭代的对象，调用对象上的Symbol.iterator方法（可迭代对象，数组，字符串等）

let arr = ["hello", "ts", "test"];for (let item of arr) {    console.log(item)}//"hello", "ts", "test"

for...of VS for...in（均可迭代一个列表。但是用于迭代的值却不同，for..in迭代的是对象的 键 的列表，而for..of则迭代对象的键对应的值。）

let list = [4, 5, 6];for (let i in list) {    console.log(i); // "0", "1", "2",}for (let i of list) {    console.log(i); // "4", "5", "6"}

let pets = {1:"Cat",2:"Dog",3:"Hamster"}for (let pet in pets) {    console.log(pet); // 1,2,3}for (let pet of pets) {    console.log(pet); // "Cat", "Dog", "Hamster"}