title: How to import library in DartPad?
body: <p>I wrote the below code in <a href="https://dartpad.dev/" rel="noreferrer">Dartpad</a> and it return me this error:</p>
  <blockquote>
  <p>Error compiling to JavaScript: unsupported import:</p>
  <p>package:collection/collection.dart</p>
  </blockquote>
  <pre><code>import &quot;package:collection/collection.dart&quot;;
  
  main(List&lt;String&gt; args) {
    
    var data = [
      {&quot;title&quot;: 'Avengers', &quot;release_date&quot;: '10/01/2019'},
      {&quot;title&quot;: 'Creed', &quot;release_date&quot;: '10/01/2019'},
      {&quot;title&quot;: 'Jumanji', &quot;release_date&quot;: '30/10/2019'},
    ];
    
    var newMap = groupBy(data, (obj) =&gt; 
                         (obj as dynamic)['release_date']
                        );
    print(newMap);
    
  }
  </code></pre>
  <p>Is there any way to resolve it?</p>