for in循环

 for in

student.age

atudent[“age”]：[ ]代表属性数组

var student = {
    name:"张三",
    sex:"男",
    age:29
};
alert(student["age"]);//显示结果是student里的age属性

for(varp instudent){
    document.write(student[p]);//显示结果是student里的所有属性
    document.write("</br>");
}