avoid_web_libraries_in_flutter

Don't use web-only libraries outside Flutter web plugins.

The analyzer produces this diagnostic when a library in a package that isn't a web plugin contains an import of a web-only library:

• dart:html
• dart:js
• dart:js_util
• dart:js_interop
• dart:js_interop_unsafe
• package:js
• package:web

When found in a package that isn't a web plugin, the following code produces this diagnostic because it imports dart:html:

import 'dart:html';
​
import 'package:flutter/material.dart';
​
class C {}

If the package isn't intended to be a web plugin, then remove the import:

import 'package:flutter/material.dart';
​
class C {}

If the package is intended to be a web plugin, then add the following lines to the pubspec.yaml file of the package:

flutter:
  plugin:
    platforms:
      web:
        pluginClass: HelloPlugin
        fileName: hello_web.dart

See Developing packages & plugins for more information.