完整代码如下：
<html>
<head>
<meta http-equiv='Content-Type' content='text/html; charset=gb2312'>
<title>自动检查并替换文本框内的字符_过滤字符_www.jb200.com</title>
<script>
<!-- Begin
function replaceChars(entry) {
out = "a"; // 要替代的字母
add = "z"; // 替换后的字母
temp = "" + entry;
while (temp.indexOf(out)>-1) {
pos= temp.indexOf(out);
temp = "" + (temp.substring(0, pos) + add +
temp.substring((pos + out.length), temp.length));
}
document.subform.text.value = temp;
}
// End -->
</script>
</head>
<body>
<center>
<form name="subform">
<input type=text name=text size=40 value="abcdabcd"><br>
<input type=button name=action value="Done!" onClick="replaceChars(document.subform.text.value);">
</form>
</center>
</body>
</html>