for...of for...in 的区别

var arr = ['a', 'b', 'c', 'd'];

        for (let a in arr) {
          console.log(a); // 0 1 2 3
        }

        for (let a of arr) {
          console.log(a); // a b c d
        }

for...of不能循环普通的对象，需要通过和Object.keys()搭配使用

var student={
    name:'wujunchuan',
    age:22,
    locate:{
    country:'china',
    city:'xiamen',
    school:'XMUT'
    }
}
for(var key of Object.keys(student)){
    //使用Object.keys()方法获取对象key的数组
    console.log(key+": "+student[key]);
}

// name: wujunchuan
// age: 22
// locate: [object Object]

 

 

 

 

 

总结

1. for in得到对对象的key或数组,字符串的下标
2. for of和forEach一样,是直接得到值,forEach中途不能return 或者break
3. for of不能对象用