code: func (p *WebPage) EvaluateJavaScript(script string) (interface{}, error) {
  	var resp struct {
  		ReturnValue interface{} `json:"returnValue"`
  	}
  	if err := p.ref.process.doJSON("POST", "/webpage/EvaluateJavaScript", map[string]interface{}{"ref": p.ref.id, "script": script}, &resp); err != nil {
  		return nil, err
  	}
  	return resp.ReturnValue, nil
  }
docs: // EvaluateJavaScript executes a JavaScript function.
  // Returns the value returned by the function.