for in 遍历的是当前索引，不适合遍历数组对象，返回的是数组下标。（适合遍历对象）
let arr = [
{name:'张三',age:18},
{name:'赵四',age:28},
{name:'王五',age:18}
]
for (const item in arr) {
console.log(item) // 0, 1, 2
console.log(arr[item]) // {name:'张三',..},{name:'赵四',..}{name:'王五',..}
}复制代码for of 遍历的是当前'键'值，适合遍历数组对象，返回的是数组单个对象。（适合遍历数组对象）
// 例子同上
let arr = [
{name:'张三',age:18},
{name:'赵四',age:28},
{name:'王五',age:18}
]
for (const item of arr) { // 将in 改成 of
console.log(item) // 0, 1, 2
}复制代码