JSFiddle - React, Tailwind, and code Playground

JavaScript

var myArray = [
    '_aaaa_2013-09-25_ssss9.txt',
    '_aaaa_2013-09-25_ssss8.txt',
    '_aaaa_2013-09-26_ssss1.txt',
    '_aaaa_2013-09-25_ssss10.txt',
    '_aaaa_2013-09-26_ssss2.txt',
    '_aaaa_2013-09-25_ssss13.txt',
    '_aaaa_2013-09-25_ssss5.txt',
    '_aaaa_2013-09-25_ssss6.txt',
    '_aaaa_2013-09-25_ssss7.txt'
];
myArray.sort(function (a, b) {
    var a_s = a.substring(0, a.indexOf('ssss') + 4);
    var a_n = a.substring(a.indexOf('ssss') + 4,
                          a.indexOf('.txt'));
    var b_s = b.substring(0, b.indexOf('ssss') + 4);
    var b_n = b.substring(b.indexOf('ssss') + 4,
                          b.indexOf('.txt'));
    if (a_s < b_s)
        return -1;
    if (a_s > b_s)
        return 1;
    return parseInt(a_n) - parseInt(b_n);
});
for (var i = 0; i < myArray.length; i++)
    document.getElementsByTagName('body')[0].innerHTML += (myArray[i]+ '<br/>');