Question

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

Answer 1

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(){}