Clean up and isolate js code in files select.html and listeners.html

[segun-codes]

This PR replaces PRs #1280 by @ayushkumarbhadani, #1274 & #1278 by @adityagoyal200, #1254 and #1255 by @Leeiaisabelle & #1275 by @adityagoyal200.

Fixes #1185 and #1184

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[segun-codes]

Hi @jywarren, kindly review and consider for merging, many thanks!

This PR replaces PRs #1280 by @ayushkumarbhadani, #1274, #1278 & #1275 by @adityagoyal200, #1254 and #1255 by @Leeiaisabelle which were at various levels of completion and required further actions from affected contributors but the common denominator is that none was given final landing.

The task of closing out with this PR is as agreed with @7malikk.

[7malikk]

Great work @segun-codes

[segun-codes]

Great work @segun-codes

Thanks!!!

[jywarren]

And many thanks to @ayushkumarbhadani, @adityagoyal200, and @Leeiaisabelle for their work on these, which is being combined here! ❤️ 🎉

[segun-codes]

@jywarren, do you want to review and merge now so we call it day on this?