JQuery :: How To Get Password Length On Form

How can I get password length on form in jquery? I get the password with this:
var sifra=$("#input:password").val();
But when I want to check if password is entered and length is more than 6 characters, it
doesn't work:

if(! sifra){
$("#sifra_p").show();
$("#sifra_p").html("Niste unijeli šifru!");
greska=1;
}else{
if(sifra.length < 6){
$("#sifra_p").show();
$("#sifra_p").html("Šifra mora imati bar 6 znakova!");
greska=1;
}else{
$("#sifra_p").hide();
}}

What could be a problem and what could be a solution. This kind of check works fine
for normally inputs (check, select etc).