Need for module.parent in the following node.js code

Question

const PORT = 3000;
const HOST = 'localhost';

var express = require('express'),
    http = require('http'),
    server = http.createServer(app);

var app = express();

const redis = require('redis');
const client = redis.createClient();

const io = require('socket.io');

if (!module.parent) {
    server.listen(PORT, HOST);
    const socket  = io.listen(server);

    socket.on('connection', function(client) {
        const subscribe = redis.createClient()
        subscribe.subscribe('realtime');

        ...
        ... 
        });
});
}

I stumbled upon this piece of code in one of the sites , In the above code I want to know the reason why the condition (!module.parent) is used ??? Whats the need for using it ??

Nathan Breit · Accepted Answer · 2013-09-11 07:08:16Z

1

If there is no module.parent it probably means that the module is being run on its own rather than being used in another program. If the !module.parent block is in a utility module I would guess that it is code for a test or developer tool. In a program that does stuff on it's own (e.g. a webserver), it would probably be the main entry point and the purpose of using it would be to make it possible to require components of that program without running the program.

answered Sep 11, 2013 at 7:08

Nathan Breit

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