Node JS override standard module

Question

Friend has asked an interesting question and I've tried a few things but to no avail, is there any way to override a Node JS module?

For instance, I want to override the readFile function to use an S3 bucket instead of the filesystem. I.E:

var fs = require('fs');

fs.readFile('my_text_file.txt', ...);

Actually runs something like this

FileSystem.readFile = function () {
    // Connect to S3 and retrieve remote file
}

I've tried the prototype but it seems they've set up native modules without the __proto__ object, they don't have a .constructor property that means anything to anyone.

I've thought about using Nodes VM but this is too strict as I want the user to be able to install modules via npm and use them.

The closest I've actually come is creating a new module (since I can't put a file named fs.js in my node_modules folder and require it; it just gets ignored) and just hard-setting the values of fs to what I want but this isn't quite right, I want the user to be using require('fs') and use my custom function.

Is this at all possible without compiling my own version of Node JS?

Answer 1

I feel obliged to strongly warn you against overriding native functions. That being said, this will work:

main.js:

var fs = require('fs'),
    oldReadFile = fs.readFile;

fs.readFile = function (filename, options, callback) {
  console.log('hey!');
  oldReadFile(filename, options, callback)
};

var other = require('./other');
other.test();

other.js:

var fs = require('fs');

exports.test = function () {
  fs.readFile('./main.js', {encoding: 'utf8'}, function (err, data) {
    console.log(err, data);
  });
};

You'll need to wrap your user's script with your own to first override what you want.