哥你写错代码了吧var uid = document.getElementById('txtLoginID');
var obPWD = document.getElementById("txtLoginPswd");
alert(obPWD.value.length);
alert(uid.value.length);
var obPWD = document.getElementById("txtLoginPswd");
alert(obPWD.value.length);
alert(uid.value.length);
<input type='password' id='a'>
alert($("#a").val().length);
没任何问题的