Node JS Modules

Modules

Modules are libraries of node js. Each single file in node js is considered as a module.

Like in front-end, we include Jquery library and then call jQuery functions, same in Node JS, libraries are included using module and then called. Modules are reusable in nodejs app.

Modules Example

         /* ext.js */
   
    const pi=Math.PI;
    var r=5;
    var a=pi*r*r;
    exports.area=a;

         /* test.js */
   
    const cir=require('./ext');
    console.log(`Area of circle is ${cir.area}`);

In the example above, ext.js is a module which exports area of a circle with radius 5. In our test.js file, we are including module using require function.

module.exports

module.exports or exports object is used to export data (string, number, boolean, function, array or object). To module.exports expose object it point to, and exports expose the property it point to. There are two types of modules in node js, build-in modules and custom modules.

Build-in modules

Node JS build-in modules includes http module, os modules, path module etc.

To include build-in modules, require function is used.

    const http=require('http');
    const os=require('os');
    const path=require('path');

Custom modules

Custom Modules are external .js files with exports property. Same require function is used to include custom js modules.

export using module.exports

         /* ext.js */
   
    const pi=Math.PI;
    var r=5;
    module.exports=pi*r*r;;

export using exports.property

         /* ext.js */
       
    const pi=Math.PI;
    var r=5;
    exports.area=pi*r*r;;
    exports.circumference=2*pi*r;
    

require

require function is used to include external modules in our app. For example, lets says our main file is test.js and module app.js exports a function or any other data type using exports object. See example

Import Module in Node JS

         /* ext.js */
   
    const pi=Math.PI;
    const r=5;
    exports.area=pi*r*r;;
    exports.circumference=2*pi*r;

         /* app.js */
   
    const cir=require('./ext');
    console.log(`Area of circle is ${cir.area}, and circumference is ${cir.circumference}`);

ES6 Modules in NodeJS

Node JS Also supports ES6 Modules since Node JS v12. require is Common JS Module Function used in Node as JS Lacks Modules earlier. So now we can also use ES6 Modules in Node JS.

To Use ES6 Modules in Node JS, set a property "type" with value "module" in package.json file. i.e "type": "module".

         /* ext.js */
       
    const pi=Math.PI;
    const r=5;
    const area=pi*r*r;
    export { a as area };

         /* app.js */
       
    import {a} from './ext.js';
    console.log(`Area of circle is ${a}`);