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How to use this in javascript module pattern?

I'm studying module pattern and have a question.
I want to use 'settings' anywhere.
script1.js
var MODULE = (function() {
var t = {};
this.settings = { // this == Window
users: ['john', 'emma']
}
return t;
})()
script2.js
MODULE.dom = function() {
var t = this; // this == MODULE
document.querySelector('p').textContent = t.settings.users[0]; // error
function _say() {
return t.settings.users[1] // error
}
return {
say: _say
}
}
MODULE.DOM = MODULE.dom.call(MODULE)
When use this.settings = {...}, 'this' means Window so code doesn't work.
When use t.settings = {...}, 'this' means MODULE so code works but when write MODULE in dev console, settings is exposed in MODULE variable. Is it ok?
I'd greatly appreciate any help, thank you!

When use t.settings = {...}, 'this' means MODULE so code works
That's the right way to do it.
but when write MODULE in dev console, settings is exposed in MODULE variable. Is it ok?
It's mostly OK.
If you're worried about the client being able to type in the variable name and see the code that gets run - there's no way to avoid that. They can just look at the devtools to see what the network requests are, and what is downloaded - or look at the Sources panel.
If you're worried about running into naming collisions with larger scripts, then - sometimes, libraries deliberately assign themselves to the window to allow other parts of the code to access them. Perhaps you'd like your MODULE to be like this. If not, then you should utilize JavaScript modules instead, which allow for scripts to be imported inside other scripts without polluting the global namespace at all or having any possibility of naming collisions. For example, you could do
// script1.js
export const MODULE = {
settings: {
users: ['john', 'emma'];
}
};
// script2.js
import { MODULE } from './script1.js';
// proceed to use MODULE
And you can do import { MODULE } from './script1.js'; from any script file, not just script2.js.
Personally, I consider the IIFE module pattern in JavaScript to be mostly obsolete nowadays. For any reasonable-sized script, better to write code in separate files and then import and export as needed. (A 1000 line file is somewhat hard to debug and refactor. Ten 100 line files are easier to debug and refactor.)

How to set environment variables like test environment for playwright-cucumber js

I've been using Playwright with Cucumber for e2e-automation of a react web application. This repo has been my starting point and it's been working out pretty good.
However, I'm looking for pointers on how to run these tests on different test environments - like development or QA, so that the target urls and other params vary as per the environment passed. For eg -
if (env == dev){
baseurl = dev_url
}
else{
baseurl = qa_url
}
The Cucumber documentation mentions the World parameter - an this issue looks like a similar issue, however I'm skeptical of passing a different JSON for this task.
Can this be achieved only at a Cucumber level or is there a Playwright or Node way of doing this?

As you are already using cucumber, define your world file like this:
First you can segregate your properties files into: properties-dev.json and properties-qa.json. Below code reads properties file based on env we are passing in defaultOptions object and stores entire properties file data into 'this'. Use 'this' in your hooks file and call this.keyNameForUrl to get url specific to environment.
Note: 'this' can be accessible only in world and hooks files (refer // https://github.com/cucumber/cucumber-js/blob/master/docs/support_files/world.md). If you need this data in other files, create a separate class and declare all public static varibles in it. In Hooks BeforeAll function, reassign values from 'this' to the static variables created in the class.
import { setWorldConstructor } from 'cucumber';
const fs = require('fs');
const defaultOptions = {
env: 'qa'
};
function processOptions(options) {
let envFile = 'properties-' + options.env + '.json';
let environment = JSON.parse(fs.readFileSync(envFile));
return Object.assign(options, environment);
}
function World(input) {
this.World = input;
});
Object.assign(this, processOptions(Object.assign(defaultOptions, options)), options);
}
setWorldConstructor(World);
// https://github.com/cucumber/cucumber-js/blob/master/docs/support_files/world.md

Hijacking node require even when spawning another script

I am trying to replace a specific package using
import Module from 'module';
const {require: oldRequire} = Module.prototype;
Module.prototype.require = function twilioRequire(file) {
if (file === 'the-package-of-interest) {
// return something else
}
return oldRequire.apply(this, arguments);
};
const p = require('the-package-of-interest');
// this gives me the replacement
This would work fine, but if this was placed inside a script that spawns another script, this does not work in the other script, i.e
// main.js
import Module from 'module';
import spawn from 'cross-spawn';
const {require: oldRequire} = Module.prototype;
Module.prototype.require = function twilioRequire(file) {
if (file === 'the-package-of-interest) {
// return something else
}
return oldRequire.apply(this, arguments);
};
spawn.sync('node', ['/path/to/another/script.js'], { stdio: "inherit" });
// another/script.js
require('the-package-of-interest');
// gives the original package, not the replacement
I don't suppose there is a way to spawn another script, but keep the hijacked require scope the same?

Even though mocking libraries are usually used in tests, this might be a good situation to stub another library or file you wrote with another one based on a configuration.
There are a lot of mocking libraries for node, and there's a good article which covers some of them.
The library it recommends is pretty good but you can use whatever you want to do this
Create a mock definitions file that replaces that import with the second file
First - define your mocks. You can do it in any place, this is just a setup.
Easiest way is to do this in the same file, but you can create a mock defitions file if you like
import rewiremock from 'rewiremock';
...
// by mocking the module library, you actually replace it everywhere
rewiremock('module')
.with(otherModule);
your other module need to have the same export for this to work and act with the same interface.
Replace the library based on a variable
To use, you need some sort of condition that will select if to use the original library or the second one
// This is only needed if you put the mock definitions in another file
// Just put the rest of the code under the previous snippter
// if everything is in the same file
require('<your_rewiremock_definitions_file>');
if (replaceImport) {
rewiremock.enable();
}
// run the code here
if (replaceImport) {
rewiremock.disabled();
}
Your module should be replaced everywhere by the second module.
You can use any other mocking library to do this. there's a short section at the start of the readme with different options if you want a different style or another library.
rewiremock works by replacing the node.js cache so it should change the dependency everywhere.

Best approach to passing variables between multi-file Node.js modules?

I have a Node.js module that I have kept as a single file up to this point. It's getting rather large though and has a lot of functionality in it that might be better separated into other modules. For example, separating out logging initialization and functionality into it's own module.
My module has a lot of (I want to say "global" but not really) top-level variables that lots of different functions access, use and modify. If I separate out functionality into separate files/modules and require them into my primary module, what is the proper approach to passing those variables between the modules?
For example, with everything in one module/file, it's easy to do this:
const logger = (log, message) {........}
const makeRequestHandler = (url, filepath) {
....
logger.info('some message here')
....
}
So it's pretty easy to access top-level systems like the logger. But, if I decided to split my logger and makeRequestHandler into their own modules/files, how would I handle this?
let logger = require('./mylogger') // Custom module
let makeRequest = require('./makerequest') // Another custom module
makeRequest.handler(url, filepath, logger)
This would work, but it doesn't seem elegant or optimal. It would get even more weird if I have a lot of different variables that I needed to pass in:
makeRequest.handler(url, filepath, logger, profiler, reportingBuffer, compressionHandler)
I've also considered passing stuff into the modules when requiring:
let makeRequest = require('./makeRequest')(logger)
or better yet:
let makeRequest = require('./makeRequest')(this) // I can access all variables made in my primary/top-level module
Is there an approach here that is more proper and better/easier to maintain? Is the last one the best approach?

What about a global locator pattern or service locator/service provider pattern as pointed out in comments wherein you can have something like a service registry and include these services in any module you want to use them in.
Although I am not sure about being the best solution of all, but it is easier to implement and feels like a neater solution than passing in the this context around the modules.
//logger.js
const logger = (log, message) {........}
export logger
Now, in the app file is where you can initialize the logger and other service instances and register them in the global locator
let logger = require('./mylogger') // Custom module
init() {
//init and set the logger
global.logger = new logger();
...
}
And this is how you can use it in the code to makRequest
let logger = global.logger;
const makeRequestHandler = (url, filepath) {
....
logger.info('some message here')
....
}
What I feel is problem with these solutions :
//Solution 1 : As you pointed out yourself this can get messy when number of paramters increase and is not very readable or understandable.
let logger = require('./mylogger')
let makeRequest = require('./makerequest')
makeRequest.handler(url, filepath, logger)
//Solution 2 : Passing around the `this` context is never a good idea,for keeping sensitive data independent or scope isolation
let makeRequest = require('./makeRequest')(this)
note :
This article explains some aspects of this solution in detail for your consideration.
Also there are some npm modules which provide these features like Service Locator
. HTH

Where does AWS-SDK Javascript code find its includes? [duplicate]

I'm trying to get JavaScript to read/write to a PostgreSQL database. I found this project on GitHub. I was able to get the following sample code to run in Node.
var pg = require('pg'); //native libpq bindings = `var pg = require('pg').native`
var conString = "tcp://postgres:1234#localhost/postgres";
var client = new pg.Client(conString);
client.connect();
//queries are queued and executed one after another once the connection becomes available
client.query("CREATE TEMP TABLE beatles(name varchar(10), height integer, birthday timestamptz)");
client.query("INSERT INTO beatles(name, height, birthday) values($1, $2, $3)", ['Ringo', 67, new Date(1945, 11, 2)]);
client.query("INSERT INTO beatles(name, height, birthday) values($1, $2, $3)", ['John', 68, new Date(1944, 10, 13)]);
//queries can be executed either via text/parameter values passed as individual arguments
//or by passing an options object containing text, (optional) parameter values, and (optional) query name
client.query({
name: 'insert beatle',
text: "INSERT INTO beatles(name, height, birthday) values($1, $2, $3)",
values: ['George', 70, new Date(1946, 02, 14)]
});
//subsequent queries with the same name will be executed without re-parsing the query plan by postgres
client.query({
name: 'insert beatle',
values: ['Paul', 63, new Date(1945, 04, 03)]
});
var query = client.query("SELECT * FROM beatles WHERE name = $1", ['John']);
//can stream row results back 1 at a time
query.on('row', function(row) {
console.log(row);
console.log("Beatle name: %s", row.name); //Beatle name: John
console.log("Beatle birth year: %d", row.birthday.getYear()); //dates are returned as javascript dates
console.log("Beatle height: %d' %d\"", Math.floor(row.height/12), row.height%12); //integers are returned as javascript ints
});
//fired after last row is emitted
query.on('end', function() {
client.end();
});
Next I tried to make it run on a webpage, but nothing seemed to happen. I checked on the JavaScript console and it just says "require not defined".
So what is this "require"? Why does it work in Node but not in a webpage?
Also, before I got it to work in Node, I had to do npm install pg. What's that about? I looked in the directory and didn't find a file pg. Where did it put it, and how does JavaScript find it?

So what is this "require?"
require() is not part of the standard JavaScript API. But in Node.js, it's a built-in function with a special purpose: to load modules.
Modules are a way to split an application into separate files instead of having all of your application in one file. This concept is also present in other languages with minor differences in syntax and behavior, like C's include, Python's import, and so on.
One big difference between Node.js modules and browser JavaScript is how one script's code is accessed from another script's code.
In browser JavaScript, scripts are added via the <script> element. When they execute, they all have direct access to the global scope, a "shared space" among all scripts. Any script can freely define/modify/remove/call anything on the global scope.
In Node.js, each module has its own scope. A module cannot directly access things defined in another module unless it chooses to expose them. To expose things from a module, they must be assigned to exports or module.exports. For a module to access another module's exports or module.exports, it must use require().
In your code, var pg = require('pg'); loads the pg module, a PostgreSQL client for Node.js. This allows your code to access functionality of the PostgreSQL client's APIs via the pg variable.
Why does it work in node but not in a webpage?
require(), module.exports and exports are APIs of a module system that is specific to Node.js. Browsers do not implement this module system.
Also, before I got it to work in node, I had to do npm install pg. What's that about?
NPM is a package repository service that hosts published JavaScript modules. npm install is a command that lets you download packages from their repository.
Where did it put it, and how does Javascript find it?
The npm cli puts all the downloaded modules in a node_modules directory where you ran npm install. Node.js has very detailed documentation on how modules find other modules which includes finding a node_modules directory.

Alright, so let's first start with making the distinction between Javascript in a web browser, and Javascript on a server (CommonJS and Node).
Javascript is a language traditionally confined to a web browser with a limited global context defined mostly by what came to be known as the Document Object Model (DOM) level 0 (the Netscape Navigator Javascript API).
Server-side Javascript eliminates that restriction and allows Javascript to call into various pieces of native code (like the Postgres library) and open sockets.
Now require() is a special function call defined as part of the CommonJS spec. In node, it resolves libraries and modules in the Node search path, now usually defined as node_modules in the same directory (or the directory of the invoked javascript file) or the system-wide search path.
To try to answer the rest of your question, we need to use a proxy between the code running in the the browser and the database server.
Since we are discussing Node and you are already familiar with how to run a query from there, it would make sense to use Node as that proxy.
As a simple example, we're going to make a URL that returns a few facts about a Beatle, given a name, as JSON.
/* your connection code */
var express = require('express');
var app = express.createServer();
app.get('/beatles/:name', function(req, res) {
var name = req.params.name || '';
name = name.replace(/[^a-zA_Z]/, '');
if (!name.length) {
res.send({});
} else {
var query = client.query('SELECT * FROM BEATLES WHERE name =\''+name+'\' LIMIT 1');
var data = {};
query.on('row', function(row) {
data = row;
res.send(data);
});
};
});
app.listen(80, '127.0.0.1');

I noticed that whilst the other answers explained what require is and that it is used to load modules in Node they did not give a full reply on how to load node modules when working in the Browser.
It is quite simple to do. Install your module using npm as you describe, and the module itself will be located in a folder usually called node_modules.
Now the simplest way to load it into your app is to reference it from your html with a script tag which points at this directory. i.e if your node_modules directory is in the root of the project at the same level as your index.html you would write this in your index.html:
<script src="node_modules/ng"></script>
That whole script will now be loaded into the page - so you can access its variables and methods directly.
There are other approaches which are more widely used in larger projects, such as a module loader like require.js. Of the two, I have not used Require myself, but I think it is considered by many people the way to go.

It's used to load modules. Let's use a simple example.
In file circle_object.js:
var Circle = function (radius) {
this.radius = radius
}
Circle.PI = 3.14
Circle.prototype = {
area: function () {
return Circle.PI * this.radius * this.radius;
}
}
We can use this via require, like:
node> require('circle_object')
{}
node> Circle
{ [Function] PI: 3.14 }
node> var c = new Circle(3)
{ radius: 3 }
node> c.area()
The require() method is used to load and cache JavaScript modules. So, if you want to load a local, relative JavaScript module into a Node.js application, you can simply use the require() method.
Example:
var yourModule = require( "your_module_name" ); //.js file extension is optional

Necromancing.
IMHO, the existing answers leave much to be desired.
At first, it's very confusing.
You have a (nowhere defined) function "require", which is used to get modules.
And in said (CommonJS) modules, you can use require, exports and module, WITHOUT THEM EVER BEING DEFINED.
Not that it would be new that you could use undefined variables in JS, but you couldn't use an undefined function.
So it looks a little like magic at first.
But all magic is based on deception.
When you dig a little deeper, it turns out it is really quite simple:
Require is simply a (non-standard) function defined at global scope.
(global scope = window-object in browser, global-object in NodeJS).
Note that by default, the "require function" is only implemented in NodeJS, not in the browser.
Also, note that to add to the confusion, for the browser, there is RequireJS, which, despite the name containing the characters "require", RequireJS absolutely does NOT implement require/CommonJS - instead RequireJS implements AMD, which is something similar, but not the same (aka incompatible).
That last one is just one important thing you have to realize on your way to understanding require.
Now, as such, to answer the question "what is require", we "simply" need to know what this function does.
This is perhaps best explained with code.
Here's a simple implementation by Michele Nasti, the code you can find on his github page.
Let's call our minimalisc implementation of the require function "myRequire":
function myRequire(name)
{
console.log(`Evaluating file ${name}`);
if (!(name in myRequire.cache)) {
console.log(`${name} is not in cache; reading from disk`);
let code = fs.readFileSync(name, 'utf8');
let module = { exports: {} };
myRequire.cache[name] = module;
let wrapper = Function("require, exports, module", code);
wrapper(myRequire, module.exports, module);
}
console.log(`${name} is in cache. Returning it...`);
return myRequire.cache[name].exports;
}
myRequire.cache = Object.create(null);
window.require = myRequire;
const stuff = window.require('./main.js');
console.log(stuff);
Now you notice, the object "fs" is used here.
For simplicity's sake, Michele just imported the NodeJS fs module:
const fs = require('fs');
Which wouldn't be necessary.
So in the browser, you could make a simple implementation of require with a SYNCHRONOUS XmlHttpRequest:
const fs = {
file: `
// module.exports = \"Hello World\";
module.exports = function(){ return 5*3;};
`
, getFile(fileName: string, encoding: string): string
{
// https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/Synchronous_and_Asynchronous_Requests
let client = new XMLHttpRequest();
// client.setRequestHeader("Content-Type", "text/plain;charset=UTF-8");
// open(method, url, async)
client.open("GET", fileName, false);
client.send();
if (client.status === 200)
return client.responseText;
return null;
}
, readFileSync: function (fileName: string, encoding: string): string
{
// this.getFile(fileName, encoding);
return this.file; // Example, getFile would fetch this file
}
};
Basically, what require thus does, is it downloads a JavaScript-file, evals it in an anonymous namespace (aka Function), with the parameters "require", "exports" and "module", and returns the exports, meaning an object's public functions and properties.
Note that this evaluation is recursive: you require files, which themselfs can require files.
This way, all "global" variables used in your module are variables in the require-wrapper-function namespace, and don't pollute the global scope with unwanted variables.
Also, this way, you can reuse code without depending on namespaces, so you get "modularity" in JavaScript. "modularity" in quotes, because this is not exactly true, though, because you can still write window.bla/global.bla, and hence still pollute the global scope... Also, this establishes a separation between private and public functions, the public functions being the exports.
Now instead of saying
module.exports = function(){ return 5*3;};
You can also say:
function privateSomething()
{
return 42:
}
function privateSomething2()
{
return 21:
}
module.exports = {
getRandomNumber: privateSomething
,getHalfRandomNumber: privateSomething2
};
and return an object.
Also, because your modules get evaluated in a function with parameters
"require", "exports" and "module", your modules can use the undeclared variables "require", "exports" and "module", which might be startling at first. The require parameter there is of course a pointer to the require function saved into a variable.
Cool, right ?
Seen this way, require looses its magic, and becomes simple.
Now, the real require-function will do a few more checks and quirks, of course, but this is the essence of what that boils down to.
Also, in 2020, you should use the ECMA implementations instead of require:
import defaultExport from "module-name";
import * as name from "module-name";
import { export1 } from "module-name";
import { export1 as alias1 } from "module-name";
import { export1 , export2 } from "module-name";
import { foo , bar } from "module-name/path/to/specific/un-exported/file";
import { export1 , export2 as alias2 , [...] } from "module-name";
import defaultExport, { export1 [ , [...] ] } from "module-name";
import defaultExport, * as name from "module-name";
import "module-name";
And if you need a dynamic non-static import (e.g. load a polyfill based on browser-type), there is the ECMA-import function/keyword:
var promise = import("module-name");
note that import is not synchronous like require.
Instead, import is a promise, so
var something = require("something");
becomes
var something = await import("something");
because import returns a promise (asynchronous).
So basically, unlike require, import replaces fs.readFileSync with fs.readFileAsync.
async readFileAsync(fileName, encoding)
{
const textDecoder = new TextDecoder(encoding);
// textDecoder.ignoreBOM = true;
const response = await fetch(fileName);
console.log(response.ok);
console.log(response.status);
console.log(response.statusText);
// let json = await response.json();
// let txt = await response.text();
// let blo:Blob = response.blob();
// let ab:ArrayBuffer = await response.arrayBuffer();
// let fd = await response.formData()
// Read file almost by line
// https://developer.mozilla.org/en-US/docs/Web/API/ReadableStreamDefaultReader/read#Example_2_-_handling_text_line_by_line
let buffer = await response.arrayBuffer();
let file = textDecoder.decode(buffer);
return file;
} // End Function readFileAsync
This of course requires the import-function to be async as well.
"use strict";
async function myRequireAsync(name) {
console.log(`Evaluating file ${name}`);
if (!(name in myRequireAsync.cache)) {
console.log(`${name} is not in cache; reading from disk`);
let code = await fs.readFileAsync(name, 'utf8');
let module = { exports: {} };
myRequireAsync.cache[name] = module;
let wrapper = Function("asyncRequire, exports, module", code);
await wrapper(myRequireAsync, module.exports, module);
}
console.log(`${name} is in cache. Returning it...`);
return myRequireAsync.cache[name].exports;
}
myRequireAsync.cache = Object.create(null);
window.asyncRequire = myRequireAsync;
async () => {
const asyncStuff = await window.asyncRequire('./main.js');
console.log(asyncStuff);
};
Even better, right ?
Well yea, except that there is no ECMA-way to dynamically import synchronously (without promise).
Now, to understand the repercussions, you absolutely might want to read up on promises/async-await here, if you don't know what that is.
But very simply put, if a function returns a promise, it can be "awaited":
"use strict";
function sleep(interval)
{
return new Promise(
function (resolve, reject)
{
let wait = setTimeout(function () {
clearTimeout(wait);
//reject(new Error(`Promise timed out ! (timeout = ${timeout})`));
resolve();
}, interval);
});
}
The promise would then normally be used like this:
function testSleep()
{
sleep(3000).then(function ()
{
console.log("Waited for 3 seconds");
});
}
But when you return a promise, you can also use await, which means we get rid of the callback (sort of - actually, it is being replaced with a state-machine in the compiler/interpreter).
This way, we make asynchronous code feel like synchronous, so we now can use try-catch for error-handling.
Note that if you want to use await in a function, that function must be declared async (hence async-await).
async function testSleep()
{
await sleep(5000);
console.log("i waited 5 seconds");
}
And also please note that in JavaScript, there is no way to call an async function (blockingly) from a synchronous one (the ones you know). So if you want to use await (aka ECMA-import), all your code needs to be async, which most likely is a problem, if everything isn't already async...
An example of where this simplified implementation of require fails, is when you require a file that is not valid JavaScript, e.g. when you require css, html, txt, svg and images or other binary files.
And it's easy to see why:
If you e.g. put HTML into a JavaScript function body, you of course rightfully get
SyntaxError: Unexpected token '<'
because of Function("bla", "<doctype...")
Now, if you wanted to extend this to for example include non-modules, you could just check the downloaded file-contents for code.indexOf("module.exports") == -1, and then e.g. eval("jquery content") instead of Func (which works fine as long as you're in the browser). Since downloads with Fetch/XmlHttpRequests are subject to the same-origin-policy, and integrity is ensured by SSL/TLS, the use of eval here is rather harmless, provided you checked the JS files before you added them to your site, but that much should be standard-operating-procedure.
Note that there are several implementations of require-like functionality:
the CommonJS (CJS) format, used in Node.js, uses a require function and module.exports to define dependencies and modules. The npm ecosystem is built upon this format. (this is what is implemented above)
the Asynchronous Module Definition (AMD) format, used in browsers, uses a define function to define modules. (basically, this is overcomplicated archaic crap that you wouldn't ever want to use). Also, AMD is the format that is implemented by RequireJS (note that despite the name containing the characters "require", AMD absolutely is NOT CommonJS).
the ES Module (ESM) format. As of ES6 (ES2015), JavaScript supports a native module format. It uses an export keyword to export a module’s public API and an import keyword to import it. This is the one you should use if you don't give a flying f*ck about archaic browsers, such as Safari and IE/EdgeHTML.
the System.register format, designed to support ES6 modules within ES5. (the one you should use, if you need support for older browsers (Safari & IE & old versions of Chrome on mobile phones/tablets), because it can load all formats [for some, plugins are required], can handle cyclic-dependencies, and CSS and HTML - don't define your modules as system.register, though - the format is rather complicated, and remember, it can read the other easier formats)
the Universal Module Definition (UMD) format, compatible to all the above mentioned formats (except ECMA), used both in the browser and in Node.js. It’s especially useful if you write modules that can be used in both NodeJS and the browser. It's somewhat flawed, as it doesn't support the latest ECMA modules, though (maybe this will get fixed) - use System.register instead.
Important sidenote on the function argument "exports":
JavaScript uses call-by-value-sharing - meaning objects are passed as a pointer, but the pointer-value itselfs is passed BY VALUE, not by reference. So you can't override exports by assigning it a new object. Instead, if you want to override exports, you need to assign the new object to module.exports - because hey, module is the pointer passed by value, but exports in module.exports is the reference to the original exports pointer.
Important sidenote on module-Scope:
Modules are evaluated ONCE, and then cached by require.
That means all your modules have a Singleton scope.
If you want a non-singleton scope, you have to do something like:
var x = require("foo.js").createInstance();
or simply
var x = require("foo.js")();
with appropriate code returned by your module.
If you need CommonJS-support for the browser (IE5+, Chrome, Firefox),
check out my code in my comment on Michele Nasti's project

You know how when you are running JavaScript in the browser, you have access to variables like "window" or Math? You do not have to declare these variables, they have been written for you to use whenever you want.
Well, when you are running a file in the Node.js environment, there is a variable that you can use. It is called "module" It is an object. It has a property called "exports." And it works like this:
In a file that we will name example.js, you write:
example.js
module.exports = "some code";
Now, you want this string "some code" in another file.
We will name the other file otherFile.js
In this file, you write:
otherFile.js
let str = require('./example.js')
That require() statement goes to the file that you put inside of it, finds whatever data is stored on the module.exports property. The let str = ... part of your code means that whatever that require statement returns is stored to the str variable.
So, in this example, the end-result is that in otherFile.js you now have this:
let string = "some code";
or -
let str = ('./example.js').module.exports
Note:
the file-name that is written inside of the require statement: If it is a local file, it should be the file-path to example.js. Also, the .js extension is added by default, so I didn't have to write it.
You do something similar when requiring node.js libraries, such as Express. In the express.js file, there is an object named 'module', with a property named 'exports'.
So, it looks something like along these lines, under the hood (I am somewhat of a beginner so some of these details might not be exact, but it's to show the concept:
express.js
module.exports = function() {
//It returns an object with all of the server methods
return {
listen: function(port){},
get: function(route, function(req, res){}){}
}
}
If you are requiring a module, it looks like this:
const moduleName = require("module-name");
If you are requiring a local file, it looks like this:
const localFile = require("./path/to/local-file");
(notice the ./ at the beginning of the file name)
Also note that by default, the export is an object .. eg module.exports = {} So, you can write module.exports.myfunction = () => {} before assigning a value to the module.exports. But you can also replace the object by writing module.exports = "I am not an object anymore."

Two flavours of module.exports / require:
(see here)
Flavour 1
export file (misc.js):
var x = 5;
var addX = function(value) {
return value + x;
};
module.exports.x = x;
module.exports.addX = addX;
other file:
var misc = require('./misc');
console.log("Adding %d to 10 gives us %d", misc.x, misc.addX(10));
Flavour 2
export file (user.js):
var User = function(name, email) {
this.name = name;
this.email = email;
};
module.exports = User;
other file:
var user = require('./user');
var u = new user();