Javascript 电影和晚餐

我从movieTotal收到了我总数的NotANumber，而且我没有得到添加pricePerTicket+PricePerDining的正确值。有人能帮我找出我做错了什么吗

<script type="text/javascript">
<!--
var ticket, earlyBirdTicket, WeekDinner, weekendDinner, numberOfTickets, TotalDue;
var numberOfTickets, pricePerTicket, pricePerDinner, costOfDandT, totalAmountOwed;
var totalDandT, yes, week, movieTotal;
var ticket = 5;
var nightTicket = 10;
var weekDinner = 8;
var weekendDinner = 12;
var yes = ticket;
var week = weekDinner;
var movieTotal = totalDandT * numberOfTickets; 
totalDandT = pricePerDinner + pricePerTicket;
numberOfTickets = prompt ("How many tickets?");
pricePerTicket = prompt ("Is this earlybird? yes/no ");
pricePerDinner = prompt ("weekend or weekday? week/weekend ");
pricePerTicket = parseInt(pricePerTicket);
pricePerDinner = parseInt(pricePerDinner);
movieTotal = parseInt (movieTotal);
if (pricePerTicket = yes)
{
     pricePerTicket = ticket;
}
else
{
     pricePerTicket = nightTicket;
}
if (pricePerDinner = week)
{
     pricePerDinner = weekDinner;
}
else
{
     pricePerDinner = weekendDinner;
}
document.write ("<br>Number of tickets sold : " + numberOfTickets);
document.write ("<br>Cost per ticket tonight : $" + pricePerTicket);
document.write ("<br>Cost per dinner tonight : $" + pricePerDinner);
document.write ("<br>Cost of dinner and ticket : $" + pricePerTicket + pricePerDinner);
document.write ("<br> Your total today is $" + movieTotal);
// -->
</script>

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您尚未初始化变量。在使用它们之前，你应该这样做。

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未初始化的变量等于未定义的，所以是的。未定义加未定义不是一个数字。

我尝试切换这两个变量，但仍然得到相同的响应。谢谢。在初始化之前，我一直在使用parseint。非常感谢你