如何让js倒计时器在rails上的ruby中触发事件

I am building a Ruby on Rails app that lets a user create a workout for various durations (i.e. 30 minutes). A workout has_many exercises. Each exercise has a duration (i.e. 30 seconds). I want the workout to loop through a random array of exercises until the timer runs out.I am building a Ruby on Rails app that lets a u