Difference between two dates in Javascript with demo

Enter values in mm/dd/yy hh:mm:ss format
First date and time
Second date and time
Result
In (decimal) hours
In (decimal) minutes
In seconds

Code:
<script type='text/javascript'>

function p (i){

return Math.floor(i / 10) + "" + i % 10;

}

function trunc (i){

var j = Math.round(i * 100);

return Math.floor(j / 100) + (j % 100 > 0 ? "." + p(j % 100) : "");

}

function calculate (form){

var date1 = new Date(form.date1.value);

alert(form.date1.value+"\n\n"+date1)

var date2 = new Date(form.date2.value);

var sec = date2.getTime() - date1.getTime();

if (isNaN(sec)){

alert("Input data is incorrect!");

return;

}

if (sec < 0){

alert("The second date ocurred earlier than the first one!");

return;

}

var second = 1000, minute = 60 * second, hour = 60 * minute, day = 24 * hour;

form.result_h.value = trunc(sec / hour);

form.result_m.value = trunc(sec / minute);

form.result_s.value = trunc(sec / second);

var days = Math.floor(sec / day);

sec -= days * day;

var hours = Math.floor(sec / hour);

sec -= hours * hour;

var minutes = Math.floor(sec / minute);

sec -= minutes * minute;

var seconds = Math.floor(sec / second);

form.result.value = days + " day" + (days != 1 ? "s" : "") + ", " + hours + " hour" + (hours != 1 ? "s" : "") + ", " + minutes + " minute" + (minutes != 1 ? "s" : "") + ", " + seconds + " second" + (seconds != 1 ? "s" : "");

}

</script>

<form id="form">

<table cellpadding="3">

<tr>

<td colspan="2" align="center">Enter values in <font color="#800000">mm/dd/yy hh:mm:ss</font> format</td>

</tr>

<tr>

<td>First date and time</td>

<td><input type="text" name="date1" /></td>

</tr>

<tr>

<td>Second date and time</td>

<td><input type="text" name="date2" /></td>

</tr>

<tr>

<td colspan="2" align="center"><input type="button" name="submit" value="Calculate" onclick="calculate(this.form)" /></td>

</tr>

<tr>

<td>Result</td>

<td colspan="2"><input type="text" name="result" readonly="readonly" size="40" /></td>

</tr>

<tr>

<td>In (decimal) hours</td>

<td colspan="2"><input type="text" name="result_h" readonly="readonly" /></td>

</tr>

<tr>

<td>In (decimal) minutes</td>

<td colspan="2"><input type="text" name="result_m" readonly="readonly" /></td>

</tr>

<tr>

<td>In seconds</td>

<td colspan="2"><input type="text" name="result_s" readonly="readonly" /></td>

</tr>

</table>