CODEWITHSUNDEEP
javascriptnode.jsprototype-programming
Bailey Parker
Bailey Parker

Reputation: 15903

Prototyping Built-In Modules in NodeJS

I've been trying to add some convenience functions to Node's file system module (mainly because it lacks some common sense things), but every time I begin fs.prototype.myfunc = in the repl, Node complains that I am trying to set a property of an undefined variable. Is it really true that you cannot access Node's built-in module prototypes from the outside? If so, does anyone know a feasible workaround to extend Node's built-in modules?

Just to note: I did require fs before trying to prototype it!

var fs = require('fs');
fs.prototype.myfunc = function() {}; //TypeError thrown here

Upvotes: 2

Views: 2765

Answers (3)

Geoff Chappell
Geoff Chappell

Reputation: 2442

What you get back in response to a require('') depends upon the particular module. Some modules do this:

module.exports = function() {}

in that case, the value returned would be function and so would have a prototype you could attach things to.

Other modules just set values on the already existing exports.module object. E.g:

module.exports.someFunc = function(){}

where module.exports is essentially just:

module.exports = {}

In the case of the fs module they do the latter:

var fs = exports;

....

fs.readFileSync = function(path, encoding) {

So you get the error you do since the object returned isn't a function. You'd get the same error if you did this:

var x = {};

x.prototype.myfunc = function(){}

Note you can just do:

var fs = require('fs');

fs.myFunc = function(){}

Upvotes: 6

Harry
Harry

Reputation: 54999

Here's an example of how to do it:

https://github.com/mikeal/node-utils/blob/master/file/lib/main.js

Upvotes: 1

Tobu
Tobu

Reputation: 25436

There might be a workaround, but node is sending you a message by not letting you monkey patch its modules. Doing require('fs-monkeypatch') to get extra functions in require('fs') is confusing. Just add your functions outside of the fs module.

Upvotes: 1

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