JavaScript 学习笔记（七）for(var i in username) {……}、.length、isNaN(……)

function check() {var username = document.myform.username.value;var password = document.myform.password.value;var repassword = document.myform.repassword.value;var email = document.myform.email.value;var education = document.myform.education.value;var year = document.myform.year.value;var day = document.myform.day.value;if(username=="") {alert("用户名不能为空");document.myform.username.focus();return false;}  //for(var i=0;i<username.length;i++){ for(var i in username) {var c = username.charAt(i);if((c<'0'||c>'9')&&(c>'z'||c<'a')&&c!='_') {alert("用户名必须由数字、字母或下划线");document.myform.username.focus();return false;}}if(password=="") {alert("密码不能为空");return false;}if(password.length<6) {alert("密码长度不能少于六位");return false;}if(repassword!=password) {alert("两次输入的密码不一致");return false;}if(email.indexOf("@")==-1||email.indexOf(".")==-1) {alert("邮箱格式不正确");return false;}if(isNaN(year)==true) {alert("年份不是数字");}if(isNaN(day)==true) {alert("日期不是数字");}var now = new Date();var nowyear = now.getFullYear();if(year>nowyear||year<1990) {alert("年份必须在1990到" + nowyear + "之间");return false;}if(education==-999) {alert("请选择学历");return false;}return true;}function clearyearText() {var obj = document.myform.year;obj.value="";}function cleardayText() {var obj = document.myform.day;obj.value="";}

<script src="check.js"></script>

<form name="myform" onsubmit="return check()" method="post"><table><tr><td>用户名</td><td><input type="text" name="username" /></td></tr><tr><td>密  码</td><td><input type="password" name="password" /></td></tr><tr><td>确认密码</td><td><input type="password" name="repassword" /></td></tr><tr><td>电子邮件</td><td><input type="text" name="email" /></td></tr><tr><td>性别</td><td><input type="radio" name="sex" checked="checked" />女<input type="radio" name="sex" />男</td></tr><tr><td>爱好</td><td><input type="checkbox" name="like" />艺术<input type="checkbox" name="like" />教育<input type="checkbox" name="like" checked="checked" />军事<input type="checkbox" name="like" />科学</td></tr><tr><td>头像</td><td><input type="file" name="photo" /></td></tr><tr><td>出生日期</td><td><input type="text" name="year" size="4" value="yyyy" onfocus="clearyearText()" />年<select name="month"><option value="-999">请选择</option><option value="1">一月</option><option value="2">二月</option><option value="3">三月</option></select><input type="text" name="day" size="4" value="dd" onfocus="cleardayText()" />日</td></tr><tr><td>学历</td><td><select name="education"><option value="-999">请选择</option><option value="0">高中</option><option value="1">专科</option><option value="2">本科</option></select></td></tr><tr><td>备注</td><td><textarea name="remark" cols="20" rows="5"></textarea></td></tr><tr><td colspan="2"><input type="submit" value="提交" /></td></tr></table></form>