问为混合web /移动颤动项目导入js.dart和html.dart

EN

import 'dart:html' as html;
import 'package:js/js.dart';
import 'package:flutter/material.dart';

@JS('loadPlayer')
external String loadPlayer();

class WebVersion extends StatelessWidget {
  const WebVersion({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    // Use the HTML package and return an HtmlElementView
  }
}

class MobileVersion extends StatelessWidget {
  const MobileVersion({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Text("Mobile version")
  }
}

Error: Not found: 'dart:js'

Error: Not found: 'dart:html'

import 'package:flutter/material.dart';


Widget getPlayer() => throw UnsupportedError("This is a stub");

import 'package:mypackage/player_stub.dart'
  if (dart.library.io) 'package:mypackage/mobile_player.dart'
  if (dart.library.js) 'package:mypackage/web_player.dart';

class Player extends StatelessWidget {

  const Player ();

  @override
  Widget build(BuildContext context) {
    return getPlayer();
  }
}

Widget getPlayer() => MobilePlayer();

Widget getPlayer() => WebPlayer();