how to add new ID to web element in .js file

I am working on testing an application with ruby and cucumber framework,in the framework are many java script files describing every action in the application and every elements ID, Class names, etc. a tester i need to go into the java script files and add unique ID s to every element i have to capture (data-test-id)so that i have a stable test case which does not break with new builds.I am not too familiar with javascript, what is the best way to do this, how do i know where i need to add the ID ?