Module Keyword in Nodejs

In the next video, you will learn what modules are, in general, and also understand the module keyword.

In the previous video, you learnt about the function wrapper. You also looked at the various parameters of the function wrapper, including exports, require, module, __filename and __dirname. You learnt that the variables are scoped locally to a module rather than being scoped globally. 

In the following video, you will learn about the module keyword.

In the video above, you learnt about the module keyword, which refers to the object representing the current module. Let's now look at how to export variables and functions from a module using the exports property of the module object.

In the video above, you learnt how to export something from a module. You looked at two methods to export: one using the . (dot) notation and the other using the [] (square bracket) notation.

The code that you looked at in the previous video is given below:

circle Module (Dot Notation):

const PI = 3.14;
const calculateArea = r => PI * r * r;
const calculateCircumference = r => 2 * PI * r;

module.exports.calculateArea = calculateArea;
module.exports.calculateCircumference = calculateCircumference;

In the code snippet given above, you can see that you have used the 'dot' notation to export the functions calculateArea and calculateCircumference.

circle Module (Bracket Notation):

const PI = 3.14;
const calculateArea = r => PI * r * r;
const calculateCircumference = r => 2 * PI * r;

module.exports['calculateArea'] = calculateArea;
module.exports['calculateCircumference'] = calculateCircumference;

In the code snippet given above, you can see that you have used the 'bracket' notation to export the functions calculateArea and calculateCircumference.

In this segment, you learnt the following:

1. Modules: Each file in Node.js is referred to as a module.

2. Before executing the code written in a module, Node.js takes the code written in the module and converts it into a function wrapper, which has the following syntax:

(function(exports, require, module, __filename, __dirname) {

   // Module code actually lives in here

});

3. The function wrapper ensures that all the code written inside a module is private to it unless explicitly stated otherwise (exported). The parameters exports, require, module, __filename, and __dirname act as the variables global to the entire code in a module. Since each module has its own function wrapper, the code written inside one function wrapper becomes local to that module and is not accessible inside another function wrapper (read module). 

4. The module keyword refers to the object representing the current module and has a property called exports. module.exports is another object that is used for defining what is exported by a module, which can be made available to other modules. In short, if a file wants to export something, it has to declare it using the module.export syntax.