Javascript Prompt Box Loops

Something is wrong with this code but I can't figure out what it is. The page does not work properly or do what it's supposed to. I need a code that prompts for a password and that limits the attempts to 3. After the third attempt, it needs to have an alert box. I'm not adding what comes after the alert box yet.

<script>
var attempts = 3;
var answer = prompt("Password: ");
while (attempts != 0) 
{
    if (answer == "Psycho")
    {
        document.write("These are pictures of my kitten and     her things.");
    }
    else
    {
        answer = prompt("Password: ");
        attempts--;
    }
}
if (attempts = 0) 
{
    alert("Incorrect Password");
}
</script>