A JavaScript Testing Developer designs and executes testing protocols for JavaScript applications to ensure their functionality and efficiency. They write and maintain test cases, automate testing processes, and identify and document bugs. They use testing frameworks such as Jest or Mocha to simulate user interactions and validate results. They also collaborate with other developers to debug and resolve issues, while striving to improve testing strategies. Additionally, they may be involved in the development process, contributing to the creation of clean, efficient code. Their goal is to ensure the delivery of high-quality, error-free JavaScript applications.