Question

Sadly I’m not a jQuery/JavaScript guru and I’m stumped with a problem.

In short, there’s going to be an event where the price of a few fixed items goes down by the minute between two dates.

For example:

2012 07 25 - $1500 -> 2012 08 01 - $1000

And my problem is I don’t even know where to start with making this a real-time countdown. Only the price is needed to appear. Any help, pointers, alternatives would be a great help.

Thanks to the replies I was able to create a solution. Sadly the pure JS version which Esailija supplied didn’t want to work, but based on that I was able to create a php/ajax solution for this. Yes, I know this will put a strain on the server, but the JS version showed a whole new set of numbers not defined in the range, but php with the same formula produced valid results. Below you can find the full php code for this.

<?php

$dateStart = strtotime("16 july 2012 00:00");
$dateEnd = strtotime("18 july 2012 9:30");
$curDate = strtotime("now");

$startPrice = 3628000;
$endPrice = 3499000;

$progress = ($curDate - $dateStart) / ($dateEnd - $dateStart);

$curPrice = $startPrice - ($startPrice-$endPrice) * $progress;

$curPrice = round($curPrice);

if ($dateStart > $curDate) {
   echo $startPrice;
} elseif ($curDate >= $dateEnd) {
   echo $endPrice;
} else {
   echo $curPrice;
}

?>

Answer 1

Get price like this:

function getPrice() {
    var startDate = Date.UTC(2012,06,25,0,0,0,0),
        endDate = Date.UTC(2012,07,01,0,0,0,0),
        startPrice = 1500,
        endPrice = 1000,
        rightNow = +new Date,
        progress,
        price;

    progress = ( rightNow - startDate ) / ( endDate - startDate );

    if( progress < 0 ) {
        price = startPrice;
    }
    else if( progress >= 1) {
        price = endPrice;
    }
    else {
        price = startPrice - Math.abs(startPrice-endPrice) * progress;
    }
}

If right now is less than startDate, price is 1500.
If right now is more than endDate, price is 1000
If right now is between, it is calculated

Demo: http://jsfiddle.net/5v4yh/1/

Demo uses 2012 07 10 - $1500 -> 2012 07 15 $1000 so it’s in the calculation phase