Feature detection

[mnordine]

Let's say we have the following:

import 'package:web/web.dart';

Future<void> main() async {
  window.navigator.vibrate([400] as VibratePattern);
}

Not all browsers have vibrate() on navigator. What's the best way to detect this?

import 'dart:js_interop_unsafe';

import 'package:web/web.dart';

Future<void> main() async {
  if (window.navigator.has('vibrate')) {
    window.navigator.vibrate([400] as VibratePattern);
  }
}

?

[kevmoo]

We likely need to make a list of these features and add some logic to generate "checkers"

CC @srujzs

See also https://github.com/dart-lang/web/issues/175

[kevmoo]

@mnordine – has is a pretty good idea. We're discussing discoverability here!

[ditman]

I'd be happy with has in JSObject (similar to JS' in?)

[srujzs]

I'd be happy with has in JSObject (similar to JS' in?)

Yup, and that's what the implementation of hasProperty (and by extension, has) does.

The downside is having to use a String instead of a Dart symbol, but I don't think we can do better. One suggestion was generating a symbol for each member but that's a lot of extra code and bloats the package quite a bit. We could imagine some API that takes a member tear-off as an argument instead of a String like has, but tear-offs are disallowed and only methods can be torn-off anyways.

[ditman]

@srujzs can a version of has be moved to somewhere that doesn't have "unsafe" in the name? :P

[srujzs]

It's a good question. :) A lot of the members in dart:js_interop_unsafe exist there because getting/setting/calling arbitrary properties is potentially unsafe from a security perspective. However, querying whether an arbitrary property exists in an object is probably always okay, and therefore has and hasProperty may be able to be moved to dart:js_interop. I should verify with someone who knows more before I do that. FWIW, the library documentation says usage of the library is fine as long as strings are statically analyzable, but maybe the dart.dev documentation should make that clear too.