script非常重要

/先声明变量/ /* var name; / / 再赋值 从右到左*/ /字符串类型要用双引号或者单引号来括起来/ /* name = "龙泉驿" alert(name); */

    /* 同时声明变最并赋值 */
    /*   var age = 18;
      alert(age); */

    /*声明多个变量*/
    /* 用var关键字来声明变量 */
    /*  var name, age, sex;
     name = "张三";
     sex = "女";
     document.write(name)
     document.write(age)
     document.write(sex) */

    /*    var b = "张三", age = 18, sex = "女";
       console.log(b)
       console.log(age)
       console.log(sex) */

    /*var a;*/
    /*控制台的打印方法*/
    /*已经声明但是没有被赋值就会默认给个undefined */
    /* console.1og(a) */

      var name, age, sex;
         name = "学号";
         age="语文成绩"
           sex = "数学成绩";
           document.write(name)
           document.write(age)
           document.write(sex)
        
           var b = "学号", age = 语文成绩, sex = "数学成绩";
        console.log(b)
        console.log(age)
        console.log(sex) 

    /*不声明直接赋值*/
    /* var userage ="123";
    document,write(userage) */

    let username = "afd"
    console, console.log(username);
    var user = "张三"
    var user = "李四"

    /*使用let定义的user是不能够被重复的声明的而var可以被重复声明*/
    /* let比var更加的严谨*/
    /*开发者a写的*/
    /* let user = '张三'; */
    /*开发者b写的时候发现报错了，不能再写user这个变量*/
    /* let user = '李四';
    document . write(user); */