Create shorten URL like counting in base 62

URLSequenceShortener.js

var shortener = function(seq) {
    var new_str = "";
    var chars = "abcdefghijklmnopqrstuvxzwyABCDEFGHIJKLMNOPQRSTUVXZWY1234567890";
    while (seq > 0) {
        var k = seq % chars.length;
        if (k == 0) {
            k = 62;
            seq--;
        }
        seq = Math.floor(seq / chars.length);
        new_str += chars[k - 1];
    }
    return new_str;
};