JavaScript

       Js

一 : 基基础

1.输出:

              alert() :控制台弹窗

              document.write("") : 在网页中书写内容

              console.log : 日志 用来调Bug

       2.变量:

              var :全局变量

                     var a = "AAA";

              let :变量

                     let a = "DYS";

            命名规范:

                     在js中可以自主命名的都可以称之为标识符

                     命名标识符的规则

                     1.不能数字打头

                     2.可以是字母,数字,符号...

                     3.不能是关键字

                     4.驼峰命名法 第一个单词小写后面单词大写

              数据类型:

                     1.undefind 只声明但是没赋值

                     2.number 用来存放数子 整数 小数

                     3.string 用来存放字符串 js中没有char类型 不管 "" '' 都是字符串

                     4.boolean只有真和假

5.null 定义一个空的对象 里面没任何东西

                 可以使用 typeof 方法来查看数据类型

                     alert(typeof a);

                 算数运算符: 加减乘除

                     +-*/

                 运算符: 或与非

                     ||   &&  !

              对象 : 万物皆对象!

                     创建对象 : new

                            let obj = new Object();

                     添加属性 :

                            obj.name = “张三”;

                            …

                           

                     查看对象属性:

                            console.log(obj.name);

                     修改属性:

                            obj.name = “李四”;

                    

删除属性:

                            Delete obj.name;

                     字面量创建对象:

                            Let obj ={

Name : “张三”

Age:15;

…

}

                    三目运算:

                            三目运算符:

                                   Let a = 10;

                                   Let b = 20;

                                   Document.write(a>b ? “D” : “G”)

                            字符串转数子:

                                   Let a = “20”;

                                   Let b = Number(a)

                            数子转字符串:

                                   Let c = 10;

                                   Let d = String(c);

              3.数组(Array本身也是一个对象)

                  创建数组:

                       Let arr = new Array()

                  添加元素:

                            数组[索引] = ;

                            arr[0] = 11;

                            arr[1] = 22;

                            arr[…] = …;

       二.循环:

             1.for循环

                  For(i=1; 1<=10; i++){

                            Alert(“hello”);

};

2.while循环:

      Let I = 1;

       While(i<=10){

       Document.writeln(“hello”)

};

      三判断:

1. If判断:

let A =parseInt(prompt("请输入一个数"));

if(A>=10){

        alert(“hi”);

}else{

        Alert(“G”)

}

let B =parseInt(prompt("请输入一个数"));

if(B>=10){

        alert(“hi”);

}else if(B>=20){

        Alert(“HHH”)

}

1. Switch 判断
   1. Let A = parselnt(prompt(“请输入要选择的数”))

Switch(A){

       case 1:

              alert(“你选择了1”);

                                   break;

                                   case 2:

                                          alert(“你选择了2”)

                                   break;

}