What sets apart initializing an Express app using "app = new Express()" compared to "app = express()"?

Question

What sets apart initializing an Express app using "app = new Express()" compared to "app = express()"?

Throughout my experience, express apps have always been initialized like this:

var express = require('express')
var app = express()

However, today I came across an example where a new operator was used:

var Express = require('express')
var app = new Express()

Is there a difference between the two methods?

Source: https://github.com/erikras/react-redux-universal-hot-example/blob/0d7c49318a8ed78bdef4022b9f0adc4bfb04bdba/src/server.js#L25

javascript express

Answer 1

Answer №1

In my opinion, there exists a subtle distinction, but one that may not have much impact in this specific scenario.

When utilizing the require statement in Node.js, what you ultimately receive is the object that the module assigns to module.exports. This could be anything from a simple value to a function.

For example, consider having the following module defined in myModule.js:

function complexOperation() { 
   // code here 
}
module.exports = complexOperation;

Upon executing:

var myModule = require("myModule.js");

You will have myModule set to complexOperation, which can then be called like a regular function. It's straightforward. However, using new complexOperation() may not always be appropriate depending on what complexOperation does.

In the case of Express.js, the returned object itself is a function called

createApplication</code (defined here: <a href="https://github.com/strongloop/express/blob/master/lib/express.js" rel="nofollow">https://github.com/strongloop/express/blob/master/lib/express.js</a>). Therefore, <code>require('express')

returns a function assigned to

express</code, which is then executed on the next line resulting in <code>app

holding the output of createApplication.

The second approach involves using the new keyword, where:

var a = new Something();

Something should be a constructor function. This statement creates a new object, calls Something() with this referring to the new object, and returns the outcome of Something().

In the given context, var app = new Express() generates a fresh object, invokes Express() with this linked to the newly created object, and then stores the result.

In the context of Express.js, since the exported item is a function, a similar outcome ensues. A new object is generated, createApplication is executed with proper setup, and then app obtains the result of createApplication.

Answer 2

In my opinion, there exists a subtle distinction, but one that may not have much impact in this specific scenario.

When utilizing the require statement in Node.js, what you ultimately receive is the object that the module assigns to module.exports. This could be anything from a simple value to a function.

For example, consider having the following module defined in myModule.js:

function complexOperation() { 
   // code here 
}
module.exports = complexOperation;

Upon executing:

var myModule = require("myModule.js");

You will have myModule set to complexOperation, which can then be called like a regular function. It's straightforward. However, using new complexOperation() may not always be appropriate depending on what complexOperation does.

In the case of Express.js, the returned object itself is a function called

createApplication</code (defined here: <a href="https://github.com/strongloop/express/blob/master/lib/express.js" rel="nofollow">https://github.com/strongloop/express/blob/master/lib/express.js</a>). Therefore, <code>require('express')

returns a function assigned to

express</code, which is then executed on the next line resulting in <code>app

holding the output of createApplication.

The second approach involves using the new keyword, where:

var a = new Something();

Something should be a constructor function. This statement creates a new object, calls Something() with this referring to the new object, and returns the outcome of Something().

In the given context, var app = new Express() generates a fresh object, invokes Express() with this linked to the newly created object, and then stores the result.

In the context of Express.js, since the exported item is a function, a similar outcome ensues. A new object is generated, createApplication is executed with proper setup, and then app obtains the result of createApplication.

What sets apart initializing an Express app using "app = new Express()" compared to "app = express()"?

Answer №1

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