This issue was originally filed by igor.ko...@mailvision.com

Example:

  bool operator==(Object o) {
    if (o is! Contact){
      return false;
    }
    Contact other = o as Contact;
    if(!areParametersEquals(other))
      return false;
    if( super!=(other) ) // !!!!!
      return false;
    return true;
  }

It works in dart, but not in dart2js:

dart2js: Error: '!=' cannot be called on super.

If change the code to
    return super==(other);
it passed compilation both in dart and dart2js

 Dart Editor version 0.8.7_r29341
 Dart SDK version 0.8.7.0_r29341
 Windows 7 32-bits