Add a way to generate JS libraries from Dart code

[shinayser]

This is a feature request.

Today Dart can be compiled to javascript via dart2js or via dartdevc but both does not provide a nice way to externalize the code for other developers to use, aka library.

Pehaps this could be an parameter addition to dartdevc, like dartdevc --library ... and then it generates the code in a externable format even easier to read, for humans .

That would complete even more tha Dart JS world and give it even more power due to the great rise of Node.Js nowadays.

[vsmenon]

This would be nice to have, but we have no near term plans for it.

[shinayser]

I understand totally. Pehaps one day :)

[vsmenon]

I should point out that Sass is probably the best example of a Dart library that's callable from JS.

They do a fair bit of heavy-lifting themselves to setup entry points, package as a Node module, etc. E.g.,:

https://github.com/sass/dart-sass/blob/master/lib/src/node.dart#L41

[mraleph]

note that @jakemac53 gave some very good arguments for why Dart might not be suitable for the task of creating libraries.

[sigmundch]

@shinayser - thanks again for following up on this in #46378

As the others mentioned, this is a hard problem and unfortunately in tension with other project goals, so just for transparency, I want to be clear that I don't believe we'll be looking at this problem any time soon.

The one recommended way to use Dart from JavaScript applications is to explicitly export the APIs via JS-interop. Today, that entails adding a main method and use it to export individual APIs using allowInterop and external setters to expose static Dart functions to your JavaScript libraries. The Sass project @vsmenon mentioned above is a great example of this.