This paper investigates the integration and assessment of IntelliGame, a gamification plugin initially designed for Java development, within the realm of JavaScript unit testing. We aim to verify the generalizability of IntelliGame to JavaScript development and to provide valuable insights into the experiment's design. For this, we first customize IntelliGame for JavaScript, and then conduct a controlled experiment involving 152 participants utilizing the Jest testing framework, and finally examine its influence on testing behavior and the overall developer experience. The findings from this study provide valuable insights for improving JavaScript testing methodologies through the incorporation of gamification.