javascript如何实现用户注册界面（附代码）

 *{
 margin: 0;
 padding: 0;
 }
 .block{
 position: relative;
 margin: 0 auto;
 margin-top: 80px;
 width: 710px;
 height: 500px;
 border: 1px solid rgba(29, 29, 29, 0.64);
 background: url("./img/logo2396.jpg")no-repeat;
 background-size: 100%;
 }
 .photo {
 position: absolute;
 z-index: 1;
 width: 710px;
 height: 500px;
 background-color: rgba(0, 0, 0, 0.71);
 }
 .biao{
 margin-top: 20px;
 position: absolute;
 z-index: 2;
 margin-left: 150px;
 }
 li{
 position: relative;
 padding-left:20px ;
 list-style: none;
 line-height: 70px;
 width: 400px;
 border: 1px solid white;
 margin:5px auto;
 }
 li input[type=text]{
 padding-left: 20px;
 border-style: none;
 background: none;
 }
 input[type=submit]{
 margin-left: 150px;
 border-style: none;
 font-size: 25px;
 color: white;
 background: none;
 }
 .d{
 background-color: rgba(222, 53, 3, 0.71);
 }
 .txt{
 line-height: 50px;
 width: 280px;
 font-size: 15px;
 color: white;
 }
 .error {
 position: absolute;
 z-index: 2;
 left: 150px;
 color: rgba(253, 253, 253, 0.4);
 font-size: 14px;
 }

<div class="block">
 <div class="photo"></div>
 <div class="biao">
 <form name="form">
 <ul>
 <li><label style="color: white">账  号：</label><input class="txt" type="text"></li>
 <li><label style="color: white">密  码：</label><input class="txt" type="text"></li>
 <li><label style="color: white">确认密码：</label><input class="txt" type="text"></li>
 <li><label style="color: white">电话号码：</label><input class="txt" type="text"></li>
 <li><label style="color: white">邮  箱：</label><input class="txt" type="text"></li>
 <li class="d"><input id="sub" type="submit" value="注册"></li>
 </ul>
 </form>
 </div>
</div>

 var sub=document.getElementById("sub");
 var txt=document.getElementsByClassName("txt");
 var li=document.getElementsByTagName("li");
 document.forms.form.onsubmit=function(){
 yan();
 var errl=document.getElementsByClassName("error").length;
 if(!errl){
 return true;
 }
 return false;
 };
 function yan(){
 for(var i=0;i<txt.length;i++){
 txt[i].focus();
 }
 sub.focus();
 }
 for(var i=0;i<txt.length;i++)
 {
 txt[i].index=i;
 txt[i].onfocus=function (){
 if(this.parentElement.children[2]==undefined) return;
 this.parentElement.children[2].remove();
 };
 txt[i].onblur=function (){
 switch (this.index){
 case 0:
 if(this.value==""){
 var s=document.createElement("span");
 s.innerHTML="请输入账号";
 s.className="error";
 li[this.index].appendChild(s)
 }
 else{
 var s=document.createElement("span");
 s.innerHTML="";
 s.className="sucess";
 li[this.index].appendChild(s)
 }
 break;
 case 1:
 if(this.value==""){
 var s=document.createElement("span");
 s.innerHTML="请输入密码";
 s.className="error";
 li[this.index].appendChild(s)
 }
 else if(this.value.length<6||this.value.length>11) {
 var s=document.createElement("span");
 s.innerHTML="密码错误";
 s.className="error";
 li[this.index].appendChild(s);
 txt[this.index].value="";
 }
 else{
 var s=document.createElement("span");
 s.innerHTML="";
 s.className="sucess";
 li[this.index].appendChild(s)
 }
 break;
 case 2:
 if(this.value==""){
 var s=document.createElement("span");
 s.innerHTML="请再次确认密码";
 s.className="error";
 li[this.index].appendChild(s);
 txt[this.index].value="";
 }
 else if(this.value!=txt[1].value){
 var s=document.createElement("span");
 s.innerHTML="请重新输入";
 s.className="error";
 li[this.index].appendChild(s);
 txt[this.index].value="";
 }
 else{
 var s=document.createElement("span");
 s.innerHTML="";
 s.className="sucess";
 li[this.index].appendChild(s)
 }
 break;
 case 3:
 if(this.value==""){
 var s=document.createElement("span");
 s.innerHTML="请输入号码";
 s.className="error";
 li[this.index].appendChild(s)
 }
 else if(this.value.length!=11){
 var s=document.createElement("span");
 s.innerHTML="号码格式错误";
 s.className="error";
 li[this.index].appendChild(s)
 txt[this.index].value="";
 }
 else{
 var s=document.createElement("span");
 s.innerHTML="";
 s.className="sucess";
 li[this.index].appendChild(s)
 }
 break;
 case 4:
 if(this.value==""){
 var s=document.createElement("span");
 s.innerHTML="请输入邮箱";
 s.className="error";
 li[this.index].appendChild(s)
 }
 else{
 var s=document.createElement("span");
 s.innerHTML="";
 s.className="sucess";
 li[this.index].appendChild(s)
 }
 break;
 }
 }
 }