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How to calculte the date a week ago

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Jan 10.2005

I am using UTC() to get the number of millisecs since Jan 1,1970 for “today”, subtracting 604800 (60*60*24*7) and using this new value (calculated as a var,lastweek) in new Date(lastweek) in order to get the date a week ago. The result I get is today’s values for the date, not those for a week ago. Please, what am I doing wrong? How can I get the date a week ago?

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JavaScript

8 Comments(s) ↴

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@ExuroJan 10.2005 — [i]Originally posted by Krumbly [/i]

[B]I am using UTC() to get the number of millisecs since Jan 1,1970 for "today", subtracting 604800 (60*60*24*7)[/B][/QUOTE]

The value [FONT=courier new]60*60*24*7[/FONT] would be the number of [i]seconds[/i] in a week, not miliseconds. You need to add a [FONT=courier new]1000*[/FONT] to the front:

<script type="text/javascript">
<!--
var today = new Date();
var lastWeek = new Date(today.getTime()-[color=red]1000*[/color]60*60*24*7);
alert("Today: " + today + "nLast Week: " + lastWeek);
//-->
</script>
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@CharlesJan 10.2005 — Another option is to use the Date object's error handling to your advantage:

[font=monospace]<script type="text/javascript">

<!--

then = new Date();

then.setDate (then.getDate() - 7);

alert (then.toDateString());

// -->

</script>[/font]
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@ExuroJan 10.2005 — I don't understand what that has to do with error handling... Would you mind explaining?

[b]Unrelated Sidenote to Charles:[/b]

I believe the title you're looking for is [i]senpai[/i] rather than [i]sempai[/i]. I don't know why it happens, but I've heard several Japanese words that get the "n" switched for an "m". For example, "numchucks" are actually "nunchucks" from the Japanese word [i]nunchaku[/i].

Just out of curiosity, are you saying you're a [i]senpai[/i] here at the forums, being one older and more experienced and lending help to those less experienced? Or does it actually have something to do with the samurai/kendo picture you have as your avatar?
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@CharlesJan 10.2005 — With the JavaScript Date object, the incorrect date "-2 January 2005" becomes 29 December 2004.

"Sempai" is how my school transliterates the word. 20 people are more senior than I on this board and only four have more posts. I needed a word that went better with my Avatar, which I picked largely because of the colors. "Sempai" seemed apt, somehow.
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@KrumblyauthorJan 10.2005 — Thanks Exuro. I wish I could claim the missing multiplier (sec to millisecs) was a deliberate error, but it was just a stupid oversight.

And thanks Charles, your:

then = new Date();

then.setDate (then.getDate() - 7);

alert (then.toDateString());

is what I wanted but couldn't get to work (I'm checking that a date entered, in a form, is at least a week ago).
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@Warren86Jan 10.2005 — <HTML>

<Head>

<Script Language=JavaScript>

var currDate = 0;

function calcJulian(isDate){

isValid = true;
tmp = isDate.split("/");
if (tmp[0] <1 || tmp[0] >12 || tmp[1] <1 || tmp[1] >31 || tmp[2] < 1970){isValid = false};
if ((tmp[0] == 4 || tmp[0] == 6 || tmp[0] == 9 || tmp[0] == 11) && tmp[1] > 30){isValid = false}
if ((tmp[0] == 1 || tmp[0] == 3 || tmp[0] == 5 || tmp[0] == 7 || tmp[0] == 8 || tmp[0] == 10 || tmp[0] == 12) && tmp[1] > 31){isValid = false}
isLeap = tmp[2]%4;
if ((tmp[0] == 2 && isLeap == 0) && tmp[1] > 29){isValid = false}
if ((tmp[0] == 2 && isLeap != 0) && tmp[1] > 28){isValid = false}
if (isNaN(Date.parse(isDate)) || !isValid){alert("Invalid Date"); return false}
else {
gregDate = new Date(isDate);
year = gregDate.getFullYear();
month = gregDate.getMonth()+1;
day = gregDate.getDate();
A = Math.floor((7*(year+Math.floor((month+9)/12)))/4);
B = day+Math.floor((275*month)/9)
isJulian = (367*year)-A+B+1721014;
return isJulian
}
}

function checkDate(isDate){

isValid = true;
if (calcJulian(isDate.value))
{
inputDate = calcJulian(isDate.value)
daysApart = currDate-inputDate;
if (daysApart < 7){isValid = false}
}
if (!isValid){alert('Invalid Date');isDate.value = ""; isDate.focus()}
if (isValid){alert('Valid Date')}
}

function getToday(){

gregDate = new Date();
year = gregDate.getFullYear();
month = gregDate.getMonth()+1;
day = gregDate.getDate();
A = Math.floor((7*(year+Math.floor((month+9)/12)))/4);
B = day+Math.floor((275*month)/9)
isJulian = (367*year)-A+B+1721014;
currDate = isJulian;
}

window.onload=getToday;

</Script>

</Head>

<Body>

<Form name='Form1'>

Input Date (mm/dd/yyyy): <input type=text size=9 name='nDate' onblur="checkDate(this)"><br>

Nothing: <input type=text size=9>

</Form>

</Body>

</HTML>
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@CharlesJan 10.2005 — [font=monospace]<script type="text/javascript">

<!--

Date.prototype.isHoliday = function () {

var holidays = [new Date ('1 January 2005'), new Date ('2 February 2005'), new Date ('25 December 2005')];

var h, i = 0;

while (h = holidays[i++]) {if (this.getTime() == h.getTime()) return true}

return false;

}

Date.prototype.isWeekend = function () {return this.getDay() == 0 || this.getDay() == 6}

Date.prototype.plusWorkDays = function (n) {

if (n == 0) return this;

var d = new Date (this.getTime());

var i = 0;

if (n > 0) {

while (i < n) {

d.setDate(d.getDate() + 1);

if (!(d.isWeekend() || d.isHoliday())) {i++}

}

} else {

while (i > n) {

d.setDate(d.getDate() - 1);

if (!(d.isWeekend()|| d.isHoliday() )) {i--}

}

}

return d;

}

alert (new Date('31 January 2005').plusWorkDays (10));

// -->

</script>[/font]
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@ExuroJan 10.2005 — [i]Originally posted by Charles [/i]

[B]With the JavaScript Date object, the incorrect date "-2 January 2005" becomes 29 December 2004.[/B][/QUOTE]
Ah, that makes sense. I love it when scripts do that! It makes coding so much easier when the dates will auto-correct themselves. Blackbox all the way!

[i]Originally posted by Charles [/i]

[B]"Sempai" seemed apt, somehow. [/B][/QUOTE]
Fine then, spurn my four years of Japanese :p
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