DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
head>
<body>
注册：<br/>
<form name="form" meethod="post" action="#">
姓名：<input name="username" type="text">*
年龄：<input name="age" type="text">*
<select name="sel_city">
<option value="0">--请选择城市--option>
<option value="北京">北京option>
<option value="上海">上海option>
<option value="广州">广州option>
select>
<input name="city" size="12" readonly="readonly" type="text">*
<input type="submit" name="btn" id="btn" value="提交">
form>
<script>
form.username.onmouseover = function(){
this.focus();
this.select();
}
form.age.onmouseover = function(){
this.focus();
this.select();
}
form.age.onkeydown = function(ev){
oEven = ev || even;
if(oEven.keyCode<48 || oEven.keyCode>57){
return false;
}
}
form.sel_city.onchange = function(){
if(this.value==0){
alert('请选择一个城市');
}else{
form.city.value = form.sel_city.value;
}
}
form.onsubmit = function(){
if(form.username.value==''){
alert('姓名为填写，无法提交');
form.username.focus();
return false;
}else if(form.age.value==''){
alert('年龄未填写，不能提交');
form.age.focus();
return false;
}else if(form.city.value=='' || form.city.value=='请选择城市'){
alert('城市未提交，不能提交');
form.sel_city.focus();
return false;
}
}
form.city.onmouseover = function(){
if(this.value==''){
this.value = '请选择城市';
}
}
script>
body>
html>