SOLVED: How to use File Object to write a MIDI syx file?

Thanks for your input KLSDIZ!

I am trying out the code but I am still struggling to find a way to replace a file with a smaller one in size, the file size doesn't change. the savedialog warns before replacing but it doesn't seem to delete the previous, instead bytes are written on top of the previous file.

Any ideas in what I could try?

Wanted to also say thanks, I was struggling to work out how to contain the data inside the JS object.
much appreciated!

ok, adding "f.eof = f.position;" before f.close(); has sorted out the resizing issue.

I have one more issue which I am trying to get my head around, its to do with filenames, specifically when writing over the same file with the same name, because I have added a .syx prefix to the JS code, when I click on the file I wish to overwrite (using the savedialog object) the filename's extension is duplicated.

I was wondering if you know of a way to strip the extensions of a file?

write file name with extension, like write MySysex-1.syx
and remove
f = new File(fn+".syx", "Midi");

Here is a working solution. I think it's pretty much done, I'm sure it can be optimised but for now it does the job. I hope it's useful to somebody!

I would really like to say thanks to everybody that helped me along the way!

--- here's the JS---

var data;

// reset data
function clear() {
    data = [];
}

// append to data
function append() {
    for(i in arguments)
        data.push(arguments[i]);
}

// replace data
function list() {
    clear();
    for(i in arguments)
        data.push(arguments[i]);
}

// write data to file
function write(fn) {
    var f = new File(fn);
    if (f.filetype == "Midi") {
        //    post("extension = .syx");
            var f = new File(fn, "write", "Midi");
    }else{
        //    post("extension = blank");
            var f = new File(fn+".syx", "write", "Midi");
         }
    if (f.isopen) {
        f.writebytes(data);
        f.eof = f.position;
        f.close();
    } else {
        error("Cannot open file: "+fn+"\n");
    }
}

// init
function loadbang() {
    clear();
}

Nice work and thank you to all who helped.

@Dan.. I was hoping I could get your email as I have some Max for Live project ideas and wondered if you would be interested in collaborating on?

Of course - dan@defectiverecords.com , and take a look at https://defectiverecords.com if you've not already...

Awesome! yeah defective, I'm familiar with it. Didn't realise you were behind it! Cool I'll drop you an email

Calling @Dan & @KLSDIZ (or anybody else with JS experience) !

I am facing an issue with the current code, which is working swell for small files but I'm working with
larger data sets now (on a different project) and it doesn't write any bytes to disk, I just get zero byte files.

I tried using the append (function in JS) and [zl group] but it crashes the patch.

Does anybody know what the size limitations for large arrays, lists are and if there's a way to work around that?

Cheers