Read a file with latest Date from a folder using JQuery

Question

I already have a folder, with the files in it with names below in a specific format i.e. MODEL_RELEASEDATE

File names in the folder named Smartphone

SmartphoneA_11122012
SmartphoneA_01022013
SmartphoneA_09102013
SmartphoneA_10072012
SmartphoneA_12042012
**SmartphoneB_08282013**
SmartphoneB_04152013
SmartphoneB_08282012
SmartphoneB_01062013
.
.
.
.
and so on

I want to write a jquery code where I can use a specific keyword from format, from above list, I will pass the value SmartphoneA and I should be able to read the file with the latest release date. Same as in case when I pass the keyword SmartphoneB.

If I pass k/w SmartphoneB, result should be served from file highlighted above, i.e. SmartphoneB_08282013

my current code reads the file name only with specific k/w. I have few alterations to be made.

<script type="text/javascript" src="http://code.jquery.com/jquery-1.10.2.min.js"></script>
<script type="text/javascript">
    var metaKeywords=$('meta[name=keywords]').attr("content");//this utility works based upon the keywords on the pages.
    var reqdKeyword = new Array();
    reqdKeyword  = metaKeywords.split(",");
    var randKeyword = reqdKeyword[Math.floor(Math.random() * reqdKeyword.length)];
    var cdnUrl = "http://abc.com/xyz/mobiles/";
    var jsnUrl = ".json?callback=showDetail";
    var finalUrl= cdnUrl.concat(randKeyword.trim()).concat(jsnUrl);


    /*

           Rest of the code goes here

    */


</script>

Answer 1

You will need a server-side code to return you a list of URIs (file names), then you can write JavaScript code to parse it (but in this case it is probably better if your server-side code will return the right name right away based on query string). In the worst case scenario you can place a dir.txt file on the server which will be listing all the files in that folder and e.g. run cron job to update it as needed.

jQuery will have no way to list remote files on the server unless your server supports it in one way or another.

Update

Once you have the file you need:

a) tokenize it into an array, e.g. like this

 var names = dir.split("\n"); 

b) leave only strings starting with keyword and cut keyword off

 names = $(names).map(function(n,i) { 
    return (n.indexOf(keyword) == 0) ?  n.split('_')[1] : null;
 }).get();

now you have an array like this ['11122012', '01022013', ...]

c) find max date in this array

var dateNum = Math.max.apply( null,
  $.map(names,function(n,i){ return parseInt(
    n.replace(/(\d{2})(\d{2})(\d{4})/, function(match, month, day, year) {
            return year + month + day;
        })) 
  }) );
var maxDate = dateNum.toString().replace(/(\d{4})(\d{2})(\d{2})/,
         function (match, year, month, day) { return month + day + year; }
       );
var fileName = keyword + "_" + maxDate;

voila, your fileName contains the name with max date.

There are other ways of doing it, e.g. really parsing the date into Date object. Also, you can simply iterate your files once, without array mapping and Math.max() iterator. As the amount of code wins over speed here, to find the optimal one depends on where you could re-use its bits and pieces without compromising maintainability.

http://jsfiddle.net/Exceeder/VLB2E/

Answer 2

The cool thing about dates is that you can easily sort them if you have the date in "descending" order (i.e., year month day hour second). Using that, we can go through your files to grab just the ones that start with the right prefix, then easily grab the latest one:

var filenames = [
        'SmartphoneA_11122012',
        'SmartphoneA_01022013',
        'SmartphoneA_09102013',
        'SmartphoneA_10072012',
        'SmartphoneA_12042012',
        'SmartphoneB_08282013',
        'SmartphoneB_04152013',
        'SmartphoneB_08282012',
        'SmartphoneB_01062013'
    ],
    whichPhone = 'SmartphoneB', // Dummy value, this would come from user interaction or whatever
    possibleFiles = [];

// This goes through your list of filenames and picks out just the ones that match `whichPhone`, then puts them into another array containing a "cleaned-up" date and some other metadata-esque stuff
for (var i = 0, j = filenames.length; i < j; i++) {
    var filename = filenames[i];

    if (filename.indexOf(whichPhone) > -1) {
        possibleFiles.push({
            index: i,
            filename: filename,
            date: parseInt(filename.split('_')[1].replace(/(\d{2})(\d{2})(\d{4})/, function(match, month, day, year) {
                return year + month + day;
            }), 10)
        });
    }
}

// Now we go through the `possibleFiles` and figure out which one has the latest date
var latestFileDate = 0,
    theActualFilenameYouWantFinally;

for (var i = 0, j = possibleFiles.length; i < j; i++) {
    var possibleFile = possibleFiles[i];

    if (possibleFile.date > latestFileDate) {
        latestFileDate = possibleFile.date;
        theActualFilenameYouWantFinally = filenames[possibleFile.index];
    }
}

// And, finally, your result
console.log(theActualFilenameYouWantFinally);

EDIT: I didn't use jQuery for this answer because meh, you don't really need jQuery for things like this. Don't get me wrong, John Resig is brilliant, and I use jQuery in almost everything, but for loops are damned fast and easy to work with, and stuff like this isn't really jQuery's strong suit anyhow.