Use operator methods in JS interop

[jodinathan]

I have built a JS bindings package that read WebIDLs and MDN to generate JS wrappers with package:js: https://pub.dev/packages/js_bindings

When I try to use the package, it throws this error while compiling:
JS interop classes do not support [] and []= operator methods.

Will you support operator methods in JS?
How can I work this around?

This tracker is for issues related to:

• dart2js
  Dart SDK version: 2.13.1 (stable) (Fri May 21 12:45:36 2021 +0200) on "macos_x64"

[sigmundch]

Thanks @jodinathan for filing this issue. I'll mark this as a duplicate of the general bug #35084 where we are tracking the general effort of revamping JS-interop using a static approach.

Many of our historical limitations (like renaming members, using operators, processing inputs and outputs) are an unfortuante result of our current implementation strategy. As I hinted in #46248, we do allow to use index operators with static extension methods. For example:

@JS()
class A { external A(); }
extension AExtension on A {
   String operator[](String y) => js_util.getProperty(this, y);
}