Let's have a file.js with this code:
module.exports.func = function(txt) {
this.a = 1;
this.b = 2;
console.log(txt, this);
return this;
}
Now we have another JS file where we do following:
var r1 = new (require('./file')).func('r1');
var r2 = new require('./file').func('r2');
In r1 case it works as intended - r1 contains reference to the newly created object.
In r2 case it does not work - r2 gets reference to module.exports from within the file.js.
The intention was to create a new object by calling func() constructor. Sure, I can do it also this way which is equal to r1:
var r3 = require('./file');
var r4 = new r3.func('r1');
However, I do not understand why r2 does not behave the same way as r1.
How do the extra parenthesis around require('./file') make a difference?
In NodeJS, require() is a built-in function to include external modules that exist in separate files. require() statement basically reads a JavaScript file, executes it, and then proceeds to return the export object.
require('express') returns a function reference. that function is called with express() . app is an object returned by express().
require() is used to consume modules. It allows you to include modules in your app. You can add built-in core Node. js modules, community-based modules (node_modules), and local modules too.
As you can see, the require function returns an object, the keys of which are the names of the variables/functions that have been exported from the required module ( circle ). In short, the require function returns the module. exports object.
These two versions are fundamentally different.
This one:
new (require('./file')).func('r1');
Executes the require, returning the exports of ./file
and then calling the new operator on the results .
This one:
var r2 = new require('./file').func('r2');
Invokes require as a constructor.
Let's look at a more isolated and simple example:
new Date() // creates a new date object
new (Date()) // throws a TypeError: string is not a function
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