Question

Month names

This follows the weekDay module almost exactly. A function expression, called immediately, wraps the variable that holds the array of names, along with the two functions that must be exported. The functions are put in an object and returned. The returned interface object is stored in the month variable.

A return to electronic life

Here is what I came up with. I’ve put parentheses around internal functions.

Module "grid"
  Vector
  Grid
  directions
  directionNames

Module "world"
  (randomElement)
  (elementFromChar)
  (charFromElement)
  View
  World
  LifelikeWorld
  directions [reexported]

Module "simple_ecosystem"
  (randomElement) [duplicated]
  (dirPlus)
  Wall
  BouncingCritter
  WallFollower

Module "ecosystem"
  Wall [duplicated]
  Plant
  PlantEater
  SmartPlantEater
  Tiger

I have reexported the directions array from the grid module from world so that modules built on that (the ecosystems) don’t have to know or worry about the existence of the grid module.

I also duplicated two generic and tiny helper values ( randomElement and Wall ) since they are used as internal details in different contexts and do not belong in the interfaces for these modules.

Circular dependencies

The trick is to add the exports object created for a module to require 's cache before actually running the module. This means the module will not yet have had a chance to override module.exports , so we do not know whether it may want to export some other value. After loading, the cache object is overridden with module.exports , which may be a different value.

But if in the course of loading the module, a second module is loaded that asks for the first module, its default exports object, which is likely still empty at this point, will be in the cache, and the second module will receive a reference to it. If it doesn’t try to do anything with the object until the first module has finished loading, things will work.

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.