Why use modules?

There are a lot of benefits to using modules in favor of a sprawling, interdependent codebase. 

• Maintainability: By definition, a module is self-contained. 
• Namespacing: In JavaScript, variables outside the scope of a top-level function are global (meaning, everyone can access them). Because of this, it’s common to have “namespace pollution”, where completely unrelated code shares global variables.
• Reusability: Let’s be honest here: we’ve all copied code we previously wrote into new projects at one point or another.