Verifying if the password field is empty
<form id="form" method="post" action="student.jsp">

          <label><strong>Username :</strong><br/><br/>
          <input type="text" value="" name="username" id="idusername">
        </label><br/><br/>

          <label><strong>Password :</strong><br/><br/>
          <input type="text" value="" name="password" id="idpassword">
            </label><br/><br/><br/>

          <input id="minibutton" name="send" type="submit" value="Login" />
        </form>

$(document).ready(function(){
//global vars
var form = $("#form");
var username= $("#idusername");
var password = $("idpassword");

//On Submitting
form.submit(function(){
    if(username.val().length==0 || password.val().length==0){
                    alert('Please enter the username');
        return false;
                    }
    else
    {
                if(password.val().length==0)
                    {
                        alert('Please enter the password');
                        return false;
                    }

                 else
                    return true;
    }
});
});

var password = $("idpassword");

var password = $("#idpassword");

if(username.val().length==0 || password.val().length==0){
    alert('Please enter the username');
    return false;
}
else{
    if(password.val().length==0)
    {
        alert('Please enter the password');
        return false;
    }
    else
        return true;
}

if(username.val().length==0){
    alert('Please enter the username');
    return false;
}
if(password.val().length==0){
    alert('Please enter the password');
    return false;
}
return true;