Extend deferred library imports to web workers

[TheOneWithTheBraid]

As of now, deferred library imports can tremendously speed up the initial load of web apps as well as the startup time of Flutter applications; they create much more modular binaries and allow to tweak performance of applications.

I would like to propose a similar approach for web worker support on web.

here, I could imagine of different approachs:

• either expose isolates to web too by implementing them to compile like deferred libraries do - into file.dart.js_N.part.js (recommended)
• compile to BLOB data URL (bad approach)

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Alternatively, it an approach with a Isolate-like API does not work, a web worker specific interface could e.g. look like:

a) (recommended)

import 'package:js/js.dart';

@JSWorker('myworker.dart')
final worker = Worker('myworker.dart.js');

b) (bad approach)

import 'myworker.dart' deferred as worker using Worker;

This option would introduce a new import syntax extension exposing a using statement followed by some helper. That sounds like a bad alternative.

I would kindly ask to discuss the provided ideas on useful web worker support, as the current way to go is neither user, nor developer friendly.

[lrhn]

I don't think adding new language features that only works on the web is going to fly.
As such, I'll move it to the SDK repository, and mark it as a request for the web compilation pipeline.

[TheOneWithTheBraid]

Couldn't Isolate.spawnUri be implemented comparably easily for web?

The provided library could be simply compiled into a standalone Dart file while having the compiler adding a corresponding communication channel using the onreceivemessage attribute from the WorkerGlobalScope?