初学正则，不太懂DOM、表单和正则的结合，请尽量详细指点一下错误的地方，谢谢！！！~~
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<title></title>
<script type="text/javascript">
<!--
function m()
{
var t=document.getElementById("a1");
var k=null;
k=t.value;
k.replace([a-z],'*');
t.value=k;
}
//-->
</script>
</head>
<body>
<input type="text" id="a1" onchange="m()" />
</body>
</html>
[解决办法]
<!DOCTYPE html><html lang="en"><head><meta charset="utf-8" /><title></title><script type="text/javascript"><!--function m(){var t=document.getElementById("a1");var k=null;//k=t.value;k=t.value.replace(/[a-z]/g,'*');t.value=k;}//--></script></head><body><input type="text" id="a1" onchange="m()" /></body></html>