require.md

Node require function

• JS files and modules are 1:1 in node

module.exports

• a POJO that always exists in a module

• that each time you subsequently require an already-required file, the exports object is cached and reused.

• modules are cached based on their resolved filename so even modules with the same name in different locations should do the right thing.

// each module exports exactly 1 object
// set the object manually
module.exports = foo;


// add a property 'blah' to the default exports object
exports blah = 12;

exports foo = 14;

// equivalent to ...
module.exports = {
    blah: 12,
    foo: 14
}

require()

• Finds and evals the javascript file (aka module)

• node core moduels are compiled into the binary

  • always preferentially loaded over files with the same names

• Each node module (a single js file) is evaluated only once - the result of evaluation is cached for subsequent uses.

• require finds files by:

  • if the file doesn't start with "./" or "/", then it is either
    1. a core module (and the local Node path is checked),
    2. a dependency in the local node_modules folder. The search for require('bar'); will start in ./node_modules
  • If the file starts with "./" it is considered a relative file to the file that called require.
  • If the file starts with "/", it is considered an absolute path. NOTE: you can omit ".js" and require will automatically append it if needed.
  • if the filename passed to require is actually a directory, it will first look for package.json in the directory and load the file referenced in the main property. Otherwise, it will look for an index.js.
  • NOTE: package.json can be involved in how require works

http://thenodeway.io/posts/how-require-actually-works/

• require loads the file into an instance of Module
• within the file that instance is available as module
• module is not a real global - you get a different instance of it within each module
• it has the properties
  • parent:
  • id:
  • exports: {}

exports

• exports starts as an alias to module.exports

  var exports = module.exports;

• if you overwrite it it will not only change exports not module.exports

// this is what your module code ends up being wrapped in before being executed
// by Module._compile()
(function (exports, require, module, __filename, __dirname) {
      // YOUR CODE INJECTED HERE!
});