Watch.JS is a small library that brings a lot of possibilities. Maybe you know the design pattern called "Observer", imagine the possibility of executing some function always that some object changes. Well, already exists other libraries that do this, but with Watch.JS you will not have to change your way to develop. Give a chance to Watch.JS, take a look at the examples and how is simple to embody Watch.JS to your routine.
//defining our object no matter which way we want