def to_html_iruby(placeholder=random_canvas_id)
      # TODO : placeholder pass, in plot#div
      @div_id = placeholder
      load_dependencies('iruby')
      chart_hash_must_be_present
      script = high_chart_css(placeholder)
      script << high_chart_iruby(extract_chart_class, placeholder, self)
      script
    end
def to_html_iruby(placeholder=random_canvas_id)
      # TODO : placeholder pass, in plot#div
      @div_id = placeholder
      load_dependencies('iruby')
      chart_hash_must_be_present
      script = high_chart_css(placeholder)
      script << high_chart_iruby(extract_chart_class, placeholder, self)
      script
    end
This method is not needed if `to_html` generates the same code. Here
 `to_html` generates the code with `onload`, so there is need of
 `high_chart_iruby` which doesn't use `onload` in chart script.