<!--输入框创建-->

账号：<input class="ipt" type="text"><br>

密码：<input class="ipt" type="password"><br>

验证码：<input id="yz_id" type="text">

<!--验证码创建-->

<div id="yzm">加载中。。请稍候</div>

<!--验证码刷新-->

<button onClick="huan()">看不清，换一张</button>

<!--验证码验证-->

<button onClick="yz()">提交</button><br>

<!--登录-->

<button onClick="denglu()">登录</button>

//全局变量

var n = 0;

//页面加载完成

window.onload=function(){

    YZMpaixu();

    huan();

}

//随机验证码生成

function YZMpaixu(n=6){

    var str = "123456789";

    var sjs = "";

    for(var i =0;i<n;++i){

        sjs += str.substr(Math.random()*str.length,1);

    }

    document.getElementById('yzm').innerHTML= sjs;

}

//验证码刷新

function huan(){

YZMpaixu(n=6)

}

//验证登陆

function denglu(){

    var ipt=document.getElementsByClassName("ipt");

    var uid = ipt[0];

    var pwd = ipt[1];

    var uidval = uid.value;

    var pwdval = pwd.value;

        if(uidval == "" || pwdval == ""){

            alert("账号或密码不能为空！");

            return;

        }

        if(uidval == "admin"){

            alert("登录成功！");

        }

}

//验证验证码

function yz(){

    var YZID=document.getElementById("yz_id");

    var yzidval = YZID.value;

        if(yzidval == ""){

            alert("验证码不能为空！");

            return;

        }

        else if(yzidval == sjs){

            alert("正确")

        }

        else{

            alert("输入错误")

        }

}

function buchong(){

    var num = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36];

    var jiguo = [];//数组定义

    var nn = 0;

    for(var i =0;i<7;++i){

//        抽取数字

        var n = parseInt(Math.random()*num.length);

//        返回抽取数在jieguo数组的首次出现位置，没有返回-1

        if(jiguo.indexOf(num[n]) < 0 ){

//        追加数字

            jiguo.push(num[n]);

        }else{

            i--;

        }

        nn++;

    }

    console.log(nn);

    console.log(jiguo);

}

<!--多选框-->

<input class="input" type="checkbox">

<input class="input" type="checkbox">

<input class="input" type="checkbox">

<input class="input" type="checkbox">

<input class="input" type="checkbox">

<input class="input" type="checkbox">

<input class="input" type="checkbox"><br>

<button onClick="quanxuan()" id="button1">全选</button>

<button onClick="fanxuan()">反选</button>

<button onClick="buxuan()">不选</button><br><br><br>

//全选

var ipt = document.getElementsByClassName("input");

function quanxuan(){

    for(var i = 0;i<ipt.length;i++){

        ipt[i].checked=true;

    }

}

//反选

function fanxuan(){

    for(var i = 0;i<ipt.length;i++){

        if(ipt[i].checked==true){

            ipt[i].checked=false;

        }

        else{

            ipt[i].checked=true;

        }

    }

}

//不选

function buxuan(){

    for(var i = 0;i<ipt.length;i++){

        ipt[i].checked=false;

    }

}

        <div onMouseOver="stop()" onMouseOut="start()"style="margin: 0 auto;width: 100%;height: 300px;position: absolute;";>

<!--        图片导入-->

        <img id="add" src="1.jpg" alt="" width="80%" height="300px">

<!--        操作按钮        -->

        <button onClick="xia()">上一页</button>

        <button onClick="zhong(0)">1</button>

        <button onClick="zhong(1)">2</button>

        <button onClick="zhong(2)">3</button>

        <button onClick="zhong(3)">4</button>

        <button onClick="shang()">下一页</button>

        </div> 

//全局变量

var IntervalObj = null;//计时器对象

var n = 0;//下表定义

var imgPath = ['1.jpg','8.jpg','12.jpg','9.jpg'];

var add = null;//图片定义

//页面加载轮播

window.onload = function(){

    add = document.getElementById("add");

//    计时器

    IntervalObj = setInterval(function(){

            add.src = imgPath[n];

            n++;

            if(n >= imgPath.length){

            n = 0;

            }

        },1000);

}

//鼠标移上停止

function stop(){

    clearInterval(IntervalObj);

}

//移走开始

function start(){

    IntervalObj = setInterval(function(){

        add.src = imgPath[n];

        n++;

        if(n >= imgPath.length){

            n = 0;

        }

    },1000);

}

//上一页

function shang(){

    n++;

    if(n >= imgPath.length){

        n = 0;

    }

    add.src = imgPath[n];

}

//下一页

function xia(){

    n--;

    if(n <=-1){

        n = imgPath.length-1;

    }

    add.src = imgPath[n];

}

//点击换页

function zhong(nn){

    add.src = imgPath[nn];

    n = nn;

}