Javascript client unable to serialize/deserialize maps with struct keys

struct Foo {
    1: required string name;
}

struct Bar {
    1: required string description;
}

struct Mapper {
    1: required map<Foo,Bar> fooToBar;
}

Mapper.prototype.write = function(output) {
  output.writeStructBegin('Mapper');
  if (this.fooToBar !== null && this.fooToBar !== undefined) {
    output.writeFieldBegin('fooToBar', Thrift.Type.MAP, 1); 
    output.writeMapBegin(Thrift.Type.STRUCT, Thrift.Type.STRUCT, Thrift.objectLength(this.fooToBar));
    // XXX
    // This will always fail as kiter8 will always be a String
    // XXX
    for (var kiter8 in this.fooToBar)
    {   
      if (this.fooToBar.hasOwnProperty(kiter8))
      {   
        var viter9 = this.fooToBar[kiter8];
        // kiter8 is a string, not an object.
        kiter8.write(output);
        viter9.write(output);
      }   
    }   
    output.writeMapEnd();
    output.writeFieldEnd();
  }
  output.writeFieldStop();
  output.writeStructEnd();
  return;
};