javascript实现把input password的默认的黑圆点变成“*”号，并保存输入值
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>asdf</title>
<script type="text/javascript" src="http://demo.jb51.net/JSlib/jquery/jquery-1.3.2.min.js"></script>
<script type="text/javascript">
$(document).ready(function () {
var i = 0;
var value="";
$("#txtCustomsCode").keyup(function (e) {//给所需要处理的文本框处理keyUp事件
e = e || window.event;
var code = e.keyCode || e.which;
if ((code >= 96 && code <= 105) || (code >= 65 && code <= 90) || (code >= 48 && code <= 57)) {//可以输入大小写字母、数字（包括小键盘）
var userkeydown = $(this).val().substr(i++);
value = value + userkeydown;
alert(value);
var reg = "*";
$(this).val($(this).val().replace(userkeydown, reg));
} else {
i = $(this).val().length;
value = value.substr(0, i);
alert(value);
}
})
})
</script>
</head>
<body>
<input type="text" name="txtCustomsCode" id="txtCustomsCode" />
</body>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>asdf</title>
<script type="text/javascript" src="http://demo.jb51.net/JSlib/jquery/jquery-1.3.2.min.js"></script>
<script type="text/javascript">
$(document).ready(function () {
var i = 0;
var value="";
$("#txtCustomsCode").keyup(function (e) {//给所需要处理的文本框处理keyUp事件
e = e || window.event;
var code = e.keyCode || e.which;
if ((code >= 96 && code <= 105) || (code >= 65 && code <= 90) || (code >= 48 && code <= 57)) {//可以输入大小写字母、数字（包括小键盘）
var userkeydown = $(this).val().substr(i++);
value = value + userkeydown;
alert(value);
var reg = "*";
$(this).val($(this).val().replace(userkeydown, reg));
} else {
i = $(this).val().length;
value = value.substr(0, i);
alert(value);
}
})
})
</script>
</head>
<body>
<input type="text" name="txtCustomsCode" id="txtCustomsCode" />
</body>
</html>
输入的字符数目没有限制。