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
        }

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]