Hello, I am getting an error message saying clock is undefined, I am not sure why, here is my code:

<script type ="text/javascript">
var theDays = new Array("Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday");
var theMonths = new Array("January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December");
var birthYear = 1960;
var birthDay = 1;
var birthMonth = 1;
var retirementYear;
var retirementAge = 65;
var timerId;
var firstDate = new Date();
var lastDate = new Date();
var minutes = 1000 * 60;
var hours = minutes * 60;
var days = hours * 24;
var years = days * 365;

function startClock()
{
	birthYear = prompt("Type the 4-digit year of your birth.");
	birthMonth = prompt("What month? (1-12)");
	birthDay = prompt("What day? (1-31)");
	retirementAge = prompt("At what age to you plan to retire?");
	retirementYear = birthYear + retirementAge;
	firstDate = new Date("birthYear", "birthMonth", "birthDay");
	lastDate = new Date("retirementYear", "birthMonth", "birthDay");
	timerId = setInterval("showTime()", 1);
}

function stopClock()
{
	clearInterval(timerId);
}

function showTime()
{
	var now = new Date();
	var seconds = ((now.getTime() + (retirementAge * 31556926000)) - now.getTime()) / 1000;
	var birthDateDisplay = "" + theDays[now.getDay()] + "," + birthDay + " " + theMonths[birthMonth] + ", " + birthYear; 
	var retirementDisplay = "" + theDays[now.getDay()] + "," + birthDay + " " + theMonths[birthMonth] + ", " + (birthYear + retirementAge);
	clock.txtSecondsFace.value = seconds;
	clock.txtMinutesFace.value = seconds / 60;
	clock.txtHoursFace.value = (seconds / 60) / 60;
	clock.txtDaysFace.value = (seconds / 60 / 60) / 24; 
	clock.txtYearsFace.value = (seconds / 60 / 60 / 24) / 365;
	clock.txtWorkDays.value = retirementForm.txtYearsFace.value * .65;
	clock.txtFunDays.value = retirementForm.txtYearsFace.value * .35;	
	clock.txtBirthDate.value = birthDateDisplay;
	clock.txtRetirementDate.value = retirementDisplay;
}

</script>


<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" />
<title>Retirement</title>
</head>

<body>

<h1>Retirement Countdown</h1>
<br />
<form name = "clock" action = "">
<p>
Click the Start Clock button to begin:
<input name = "btnStartClock" value = "Start Clock" type = "button" onclick = "startClock()" />
<input name = "btnStopClock" value = "Stop Clock" type = "button" onclick = "stopClock()" />
</p>
<p>
Birth Date:
<input name = "txtBirthDate" type = "text" />
</p>
<p>
Retirement Date:
<input name = "txtRetirementDate" type = "text" />
</p>
<p>
<h3>Countdown to Retirement</h3>
</p>
<p>
Seconds:  
<input name = "txtSecondsFace" type = "text" />
Minutes:
<input name = "txtMinutesFace" type = "text" />
</p>
<p>
Hours:
<input name = "txtHoursFace" type = "text" />
Days:
<input name = "txtDaysFace" type = "text" />
Years:
<input name = "txtYearsFace" type = "text" />
</p>
<p>
<h3>Work Days Versus Fun Days</h3>
</p>
<p>
A typical full time employee works 65 days out of every 100 days.
</p>
<p>
Work days left: 
<input name = "txtWorkDays" type = "text" />
Fun days before retirement:
<input name = "txtFunDays" type = "text" />
</p>
</form>
<p>
<h2>Now that is something to think about!</h2>
</p>

A lot of problems to begin with.

» You are accessing form elements the wrong way. Read this.

» prompt() returns a string and you are treating it as a number which in itself is introducing a lot of problems.

» setTimeout() takes it's second parameter as milliseconds and not seconds.

» I see a lot of needless calculations going on in showTime() function. Don't touch the DOM unless absolutely necessary. For eg. since we know that the value of the 'hour' text field would only change after 60 minutes, there is no point in updating it every second.

» In javascript, numbers are represented using 64 bit double precision format as per the IEEE floating point standards. Showing the amount of 'seconds' left in decimals would be not desirable. Use the toFixed() function of Number to get away with those extra digits after the dot.

Follow the suggestions, format and indent the code and come up with a fresh solution.

This question has already been answered. Start a new discussion instead.