Question

I’m creating functionality to increase the last number in a filename with 1.

Samples:

filename01.jpg    =>  filename02.jpg
file01name01.jpg  =>  file01name02.jpg
file01na01me.jpg  =>  file01na02me.jpg

I’m struggling with the cases where the original file name contains the same number two or more times. I only want to increase the last number in the filename.

I have done some research, but not been able to find a correct regex. Perhaps someone could help me.

Ideally I want my code to look something like this:

var filename = "somefilename";

var newFilename = filename.replace(regex,lastNumber + 1);

I’m not sure if it could be done this easy. But I need to figure out the regex before I move on.

---

Thanks to pivmvb, here is my final solution:

function getIncreasedFileName(fileName){
    var newFileName = fileName.replace(/(\D+)(\d+)(\D+)$/, 
        function(str, m1, m2, m3) {
            var newstr = (+m2 + 1) + "";

            return m1 + new Array(m2.length+1 - newstr.length).join("0") + newstr + m3;
        })

    return newFileName;
}

Answer 1

"test01.jpg".replace(/(\D+)(\d+)(\D+)$/, function(str, m1, m2, m3) {
    var newstr = (+m2 + 1) + "";
    return m1 + new Array(3 - newstr.length).join("0") + newstr + m3;
    // m1 === "test"
    //
    // m2 === "01"
    //   So:
    //      +m2 + 1 === 2
    //
    //      (+m2 + 1) + "" === "2"
    //         (convert to string, call this `newstr`)
    //
    //      new Array(3 - newstr.length).join("0") === "0"
    //         (this adds an appropriate amount of leading zeroes
    //         so that the total length is 2)
    //
    // m3 === ".jpg"
});

Where:

\D+   one or more non-digits
\d+   one or more digits
\D+   one or more non-digits
$     end of string (so it only matches the last digits)

Then replace the matched string by a function that returns a new string, after doing the following:

1. adding 1 to the number
2. adding leading zeroes