方法一

<script type="text/javascript">   
function password() {   
var testV = 1;   
var pass1 = prompt('请输入密码','');   
while (testV < 3) {   
if (!pass1)   
history.go(-1);   
if (pass1 == "123") {//初始密码123   
alert('密码正确');   
break;   
}   
testV+=1;   
var pass1 =   
prompt('密码错误!请重新输入:');   
}   
if (pass1!="password" & testV ==3)   
history.go(-1);   
return " ";   
}   
document.write(password());   
</script>  
<!--下面添加你要显示的内容或者代码-->

方法二

<script type="text/javascript">   
loopy()   
function loopy() {   
var sWord =""  
while (sWord != "123") {//设置密码
sWord = prompt("输入正确密码才能登陆!")   
}   
alert("欢迎访问")   
}   
</script> 
<!--下面添加你要显示的内容或者代码-->

方法三

<script type="text/javascript">   
function password() {   
var testV = 1;   
var pass1 = prompt('请输入密码:','');   
while (testV < 3) {   
if (!pass1)    
history.go(-1);   
if (pass1 == "123") {//设置密码
alert('口令正确，进行跳转');   
window.location.href="http://test.junyao2018.cn/";//添加你要跳转的页面
break;   
}    
testV+=1;   
var pass1 =    
prompt('密码错误','');   
}   
if (pass1!="password" & testV ==3)    
history.go(-1);   
return " ";   
}    
document.write(password());   
</script>