javascript equivalent of Action?

I'm trying to port some code from the audiorecorder plugin from prime31 from c# to javascript. The Author at Prime31 wasn't sure. I don't understand these lines that include ACTION. I looked up action but still don't know what would be a javascript equivalent. It looks like ACTION is defining some sort of function and putting it into a variable? I thought unityscript javascript could not do that sort of thing. Can someone help me find a javascript equivalent to these Action lines below.

         var onFailure = new Action<string>( error => Debug.Log( error ) );
             var onSuccess = new Action<AudioClip>( clip =>
             {
                 audio.clip = clip;
                 audio.Play();
             });
             StartCoroutine( AudioRecorderBinding.loadAudioFileAtPath( file, onFailure, onSuccess ) );
 
 Other relevant code:
 
 function onError( error:String)
     {
         display="error loading audio file: " + error ;
     }
     
     
     function onSuccess( clip:AudioClip )
     {
         audio.clip = clip;
         audio.Play();
     }
 
 
     public static IEnumerator loadAudioFileAtPath( string file, Action<string> onFailure, Action<AudioClip> onSuccess )
     {
         var www = new WWW( file );
         
         yield return www;
         
         if( www.error != null )
         {
             if( onFailure != null )
                 onFailure( www.error );
         }
 
         if( www.audioClip )
         {
             if( onSuccess != null )
                 onSuccess( www.GetAudioClip( false ) );
         }
         
         www.Dispose();
     }