Loading an XML file with todays date in the filename... need to fallback to old file if one with todays date doesnt exist..

Question

So here is my question. Using javascript/jQuery I am currently loading in an XML file that has a file name such as carousel_large_2010-06-08.xml.. the way I am doing it is checked for todays date then grabbing a file that has that date in the filename... the issue is sometimes they wont be uploading a new file for a given day so it needs to fallback to a older date that exists.. Wondering how to do it? Here is my code:

        // set date for xml file
        var currentTime = new Date(),
            month = currentTime.getMonth() + 1,
            day = currentTime.getDate(),
            year = currentTime.getFullYear();

        if(month.toString().length == 1){
            month = '0'+month.toString();
        }
        if(day.toString().length == 1){
            day = '0'+day.toString();
        }

        var dateObject = year+"-"+month+"-"+day;

        // start magic
        $jq.ajax({
            type: "GET",
            url: "_xml/carousel/home/carousel_large_"+dateObject+".xml",
            dataType: "xml",
            success: HPCarousels.heroCarousel.parseXML,
            error: function(){
                alert('Error Loading XML Content');
            }
        }); 

Answer 1

Here's a proposed (untested) solution. I based it largely on yours, but factored out date string calculation. Set maxOffset to the max # of days you want to look back (in your question you said yesterday, so 1)

function getDateString(offset) {

    // set date for xml file
    var currentTime = new Date().setDate(today.getDate()-offset),
        month = currentTime.getMonth() + 1,
        day = currentTime.getDate(),
        year = currentTime.getFullYear();

    if(month.toString().length == 1){
        month = '0'+month.toString();
    }
    if(day.toString().length == 1){
        day = '0'+day.toString();
    }

    return year+"-"+month+"-"+day;
}

var maxOffset = 1;
var success = 0;
for(var offset = 0; offset <= maxOffset && !success; offset++) {
    success = 1;
    // start magic
    var dateString = getDateString(offset);
    $jq.ajax({
        type: "GET",
        async: false; 
        url: "_xml/carousel/home/carousel_large_"+dateString+".xml",
        dataType: "xml",
        success: HPCarousels.heroCarousel.parseXML,
        error: function(){
            success = 0;

        }
    }); 
}
if (!success) {
    alert('Error Loading XML Content');
}

Answer 2

I'm assuming you don't know if the file is missing until the AJAX call returns, so at that point you can attempt another lookup.

function getDate(timestamp) {
    month = timestamp.getMonth() + 1,
    day = timestamp.getDate(),
    year = timestamp.getFullYear();

    return year + '-' + ((month < 10) ? '0' + month : month) + '-' + ((day < 10) ? '0' + day : day);
}

function attemptGet(timestamp, attempt) {
    if (attempt >= 3) // Maximum number of attempts
        return;
    $jq.ajax({
        type: "GET",
        url: "_xml/carousel/home/carousel_large_"+dateObject+".xml",
        dataType: "xml",
        success: HPCarousels.heroCarousel.parseXML,
        error: function(){
            if (/* file is missing */) {
                attemptGet(timestamp - 24 * 60 * 60, attempt + 1);
            } else {
                alert('Error Loading XML Content');
            } 
        }
    }); 
}
attemptGet(0);