Question

Modules provide structure to bigger programs by separating the code into different files and namespaces. Giving these modules well-defined interfaces makes them easier to use and reuse and makes it possible to continue using them as the module itself evolves.

Though the JavaScript language is characteristically unhelpful when it comes to modules, the flexible functions and objects it provides make it possible to define rather nice module systems. Function scopes can be used as internal namespaces for the module, and objects can be used to store sets of exported values.

There are two popular, well-defined approaches to such modules. One is called CommonJS Modules and revolves around a require function that fetches a module by name and returns its interface. The other is called AMD and uses a define function that takes an array of module names and a function and, after loading the modules, runs the function with their interfaces as arguments.

This is a book about getting computers to do what you want them to do. Computers are about as common as screwdrivers today, but they contain a lot more hidden complexity and thus are harder to operate and understand. To many, they remain alien, slightly threatening things.