typeof检测变量数据类型

  

  var num = 10;
    console.log(typeof num); //输出结果是number
    var str = "张三";
    console.log(str); //输出结果是string
    var flag = true;
    console.log(flag); //输出结果是boolean
    var vari = undefined;
    console.log(vari); //输出结果是undefined
    var timer = null;
    console.log(typeof timer); //输出结果是object
    //   prompt 取出来的值是  字符型
    var age = prompt("请输入年龄");
    console.log(age);
    console.log(typeof age); //输出结果是string