[chrismorgan]

And when you reimplement <select>, it won’t feel native because different platforms have different conventions (e.g. placement of dropdown, click-and-drag behaviour, whether focus is selection, keyboard shortcuts like Tab), and very few implementations try even half-baked user-agent sniffing to try to emulate the platform. And that’s just thinking about desktop platforms; on mobile platforms, the native dropdown behaviour is simply unimplementable.

I would say: if it’s just about the style of the <select>, stubbornly refuse to reimplement it, just do what you can on it with CSS and try no further. If you’re needing different functional behaviour (e.g. adding right-aligned text on each option, or making it intelligently filterable by typing—e.g. an airport picker making “CHC” match “Christchurch”), then yeah, you’ve got to reimplement <select> even though it’ll necessarily be a smidgeon worse in some ways.

<select> makes a very bad primitive.

[alpaca128]

Not only that, but reimplementations tend to have bugs. I cannot remember a single time I used YouTube's comment text field without some bug in the last 5 years. It always breaks in some way, usually when line breaks get involved. Right now when I press Return twice the cursor will only move down one line. It's been like that for at least 6 months. Now and then they replace the bug with a different one, but it never really works correctly.

[bryanrasmussen]

>and very few implementations try even half-baked user-agent sniffing to try to emulate the platform

well, to be fair every tutorial on JS for the last 16+ years or so has said avoid user-agent sniffing but only detect capabilities, not to mention freezing of user agent string will make this point moot. Problem of course being that you cannot detect how the specific browser makes a select work with capability detection.

[chrismorgan]

Freezing the user-agent string won’t prevent sniffing, it’ll just possibly make sniffing of precise version numbers a bit more difficult (… because you’ll be abusing feature detection to achieve it); but for this sort of thing you’re mostly just caring about the platform at a coarse level, and maybe the browser (though I think Edge lost its distinctive <select> style and behaviour in the Chromium migration, so that now all browsers on Windows work roughly the same). So UA freezing won’t cause any trouble at all for this sort of thing.

For various sorts of keyboard shortcuts, this style of platform detection has long been essential, so that you can use altKey/⌘ on Apple platforms and ctrlKey/Ctrl everywhere else. Ain’t never been no feature detection candidate for that.