for...in和for...of

var arr = [1,2,3]
for(var item in arr){
    
    console.log(item)}// 0 1 2
for(var item of arr){
    
    console.log(item)}// 1 2 3
var obj = {
    
    a:'11',b:'22'}
for(var item in obj){
    
    console.log(item)} // a b
for(var item of obj){
    
    console.log(item)}// 报错  
// obj is not iterable