title: Unsupported operation: _Namespace while using dart io on web
body: <pre><code>I am trying to use dart-io to read and write file. I am getting below exception.
  Uncaught Error: Unsupported operation: _Namespace
      at Object.dart.throw (dart_sdk.js:4537)
      at Function.get _namespacePointer [as _namespacePointer] (dart_sdk.js:49364)
      at Function._namespacePointer (dart_sdk.js:47224)
      at Function._dispatchWithNamespace (dart_sdk.js:47227)
      at io._File.new.open (dart_sdk.js:47342)
      at new io._FileStreamConsumer.new (dart_sdk.js:47186)
      at io._File.new.openWrite (dart_sdk.js:47468)
      at refresh (main.dart:15)
      at refresh.next (&lt;anonymous&gt;)
      at runBody (dart_sdk.js:22264)
      at Object.async.async (dart_sdk.js:22292)
      at main.refresh (main.dart:13)
      at Object.dart._checkAndCall (dart_sdk.js:4731)
      at Object.dart.dcall (dart_sdk.js:4736)
  </code></pre>
  
  <p>Code I used
      final output = io.File('output.txt').openWrite();
      output.write(output_data);</p>
  
  <pre><code>Could you please help me in fixing it.
  Or any other way to read and write files using dart in a web application.
  </code></pre>