Splits your combo URL if its length exceeds the max length limitation.

split_combo_url.js

function splitUrl(base, files, separator, maxLength) {

    base = base || "/";
    files = files || [];
    separator = separator || ",";
    maxLength = maxLength || 1024;

    var items = [],
        results = [],
        url = base + files.join(separator),
        file,
        extra = [],
        i, j;

    // Checks if url exceeds max length.
    if (url.length <= maxLength) {
        results.push(url);
        return results;
    }

    // Adds files one by one to check if it exceeds max length.
    for (i = 0, j = files.length; i < j; i += 1) {
        items.push(files[i]);
        url = base + items.join(separator);

        // Oops! It exceeds max length!!
        if (url.length > maxLength) {

            // Remove the last file from `items` array.
            file = items.pop();

            // Now we can make sure current url doesn't exceed.
            // Adds it to $results array.
            results.push(base + items.join(separator));

            // Creates new items array for next iteration.
            items = [];
            if (file) {
                items.push(file);
            }
        }
    }

    // Adds the rest files to `result` array.
    if (items.length) {
        url = base + items.join(separator);
        results.push(url);
    }

    return results;
}

split_combo_url.php

<?php

function split_combo_url($base, $files = array(), $separator = ",", $max_length = 1024)
{   
    $results = array();
    $url = $base . implode($separator, $files);

    // Checks if url exceeds max length.
    if (strlen($url) <= $max_length)
    {   
        $results[] = $url;
        return $results;
    }   

    // Adds files one by one to check if it exceeds max length.
    $extra = array();
    $len = count($files);
    for ($i = 0; $i < $len; $i++)
    {   
        $items[] = $files[$i];
        $url = $base . implode($separator, $items);

        // Oops! It exceeds max length!!
        if (strlen($url) > $max_url_length)
        {   
            // Remove the last file from $items array.
            $file = array_pop($items);

            // We can make sure current url doesn't exceed.                                                                                                                                         
            // Adds it to $results array.
            $results[] = $base . implode($separator, $items);

            // Creates the $items array for next iteration.
            $items = []; 
            if ($file) 
            {
                $items[] = $file;
            }   
        }   
    }   

    // Adds the rest files to $result array.
    if (count($items))
    {   
        $url = $base . implode($separator, $items);
        $results[] = $url;
    }   

    return $results;
}   
?>