Could you recommend a script/library for scraping in Python or Javascript?

Are you making harder work of this than you need to? My approach would be to copy+paste (scrape if you prefer) the text from the discussion thread.

For example: https://www.chess.com/votechess/game/127962

I picked move 5 (white) and copied all the comments:-

mxgolota
Jun 29, 2019
Обижаете) коль все рекомендуют кб5, то так м проголосую)

mksn_undead
Jun 28, 2019
На жаль, вельмишановне панство має звичку коментарі не читати.

TheBest1234567890
Jun 28, 2019
Вельмишановні панове ! Хід 5. К с 6 є слабким та неамбіційним , оскільки після bc чорні мають прекрасний центр та мінімальну перевагу . Прошу вас долучатися до ходу К b 5

mxgolota
Jun 28, 2019
Какие-то интересные у вас сицилианки)

nutaras

Згідно бази початків, найпопулярнішим і найвдалішим для білих є 5.Кб5

https://www.365chess.com/opening.php?m=9&n=329&ms=e4.c5.Nf3.Nc6.d4.cxd4.Nxd4.e5&ns=3.3.4.37.45.47.46.329

Isn't that what you want? I use Python for all of my activities on this site but I think trying to code for this task may be over-complicating it?

Something like this should work:

function sleep(millisec) {
    var start_time = new Date().getTime()
    while (new Date().getTime() < start_time + millisec) {}
}

pgn = window.chesscom.game.pgn.split('\n')[14].split(" ")

mvs = [] // moves

for (i = 0; i < pgn.length - 1; i++) {
    if (i % 3 != 0) {
        mvs.push(pgn[i])
    }
}


comments = []
for (i = 0; i < 5; i++) {

    comm = {}
    comm.mv = i
    comm.san = mvs[i]

    sleep(700)

    get_comments_id(comm)
}

function get_comments_id(comm_obj) {

    url = "https://" + document.location.host + document.location.pathname + "?activePagination=archive&mv=" + comm_obj.mv + "&san=" + comm_obj.san

    console.log(url)

    var xhr = new XMLHttpRequest()

    xhr.onreadystatechange = function() {
        if (xhr.readyState === 4) {

            comment_id = parse_comment_id(xhr.response)

            sleep(1000)

            get_comments(comment_id, comm_obj)

        }
    }

    xhr.open('GET', url, true)
    xhr.send('')
}


function get_comments(id, obj) {

    url = 'https://www.chess.com/callback/comments?page=1&parentId=' + id + '&forumTopicTypeCode=votechess_forum'

    var XHR = new XMLHttpRequest()

    XHR.onreadystatechange = function() {
        if (XHR.readyState === 4) {
            obj.comments = JSON.parse(XHR.response).data
            comments.push(obj)
        }
    }

    XHR.open('GET', url, true)
    XHR.send('')
}

function parse_comment_id(html) {
    rows = html.split('\n')

    for (const row of rows) {
        if (row.slice(4, 31) == "window.chesscom.commentsBox") {
            eval(row)
            return window.chesscom.commentsBox.ids.archive
        }
    }
}

alert(' all downloaded ')
console.log(comments)

If you paste it into the console at https://www.chess.com/votechess/game/127962 , it should fill the comments variable with the comments for the first 5 moves. (Well, paging is not implemented, so only the first 20.)

I haven't thought of this. It's not bad, actually. Unfortunately, this wouldn't allow me to extract the PGNs from the diagrams posted in the comments, which is something that would be very useful for me.

Thank you! I can see the comments and I can see the PGNs, too This looks like a good start for me.

O/k but you didn't include that requirement in your 'specification' above?

You're right, I didn't. Maybe I should have. It's something I can extract reasonably easily from the html content, so my question only focused on how to get the (html) content. Now that I'm writing this, I see that I should have specified at least that. But then again, if there was a library that would parse the chess.com posts into JSON or some other data structure, that would be also fine - I don't need the content to be in html per se. Anyway, I've edited the original post.

You could use requests and beautifulsoup. that's what i personally used for web scraping

Looks good, as long as I can get around the captchas. Will give it a try. Thx for the tip

You can contact support and get permission for such a bot, as long as the bot does not play games or suggest moves. I would recommend being proactive and just contacting them. 

Good idea! I'll do that.