​x
 
<html>
<head>
<script type="text/javascript">
function disablePassword()
  {
  document.getElementById("password1").disabled=true
  }
</script>
</head>
<body>
​
<form>
<input type="password" id="password1" />
<input type="button" id="button1" onClick="disablePassword()" value="Disable password field" />
</form>
​
</body>
</html>
​