What is the use of module.parent in node.js? How can I refer to the require()ing module?

Question

I was looking in the node.js module documentation, and noticed that each module has a property- module.parent. I tried to use it, but got burnt by the module caching- module.parent only ever seems to the module that first require()'d it, irrespective of current context.

So what is the usage of it? Is there any other way for me to get a reference to the current require()ing module? Right now I'm wrapping the module in a function, so that it is called like:

require("mylibrary")(module)

but that seems sub-optimal.

Answer 1

The "parent" is the module that caused the script to be interpreted (and cached), if any:

// $ node foo.js
console.log(module.parent); // `null`

// require('./foo')
console.log(module.parent); // `{ ... }`

What you're expecting is the "caller," which Node doesn't retain for you. For that, you'll need the exported function you're currently using to be a closure for the value.

Answer 2

There is a workaround for this. Node adds a module to the module cache before it finishes loading it. This means that a module can delete itself from the module cache while it's loading! Then every time the module is require'd a new instance of the module is loaded.

Magic.js

console.log('Required by ' + module.parent.filename);
delete require.cache[__filename];

Module1.js

//prints "Required by Module1.js"
require('./Magic');

Module2.js

//prints "Required by Module2.js"
require('./Magic');

Of course the side-effect of this is that your module is no longer a singleton, so you have to code Magic.js with that in mind. If you need to store global data you can always keep it in a require()'ed module that doesn't delete itself from the cache.