for in or for of

for in 取key；for of 取value

let arr = [1,2,3,4];
for(let i in arr){
    console.log(i)
}

输出: 0,1,2,3

注意：并不是1,2,3,4

let arr = [
    {id:"1",name:"lin"},
    {id:"1",name:"lin2"},
];
for(let i of arr){
    console.log(i)
}

输出：

{id: "1", name: "lin"}
{id: "1", name: "lin2"}