How to write code using module.exports in Node.js ?

module is a discrete program, contained in a single file in Node.js. They are tied to files with one module per file. module.exports is an object that the current module returns when it is "required" in another program or module.

We are going to see a simple code like the calculator to learn how to use module.exports in Node.js. I will walk you through step by step.

Step 1: Create two files "app.js" and "calculator.js" in your project folder. And initialize the project through npm in the terminal.

npm init

Step 2: Now we have a nodeJS based project with "app.js" as its entry point. Now let's first code "calculator.js". We will create a class named Calculator in it. It would have several member functions namely:

• preIncrement: For the prefix increment operation
• postIncrement: For the postfix increment operation
• preDecrement: For the prefix decrement operation
• postDecrement: For the postfix decrement operation
• add: For addition of two numbers
• subtract: For subtraction of two numbers
• multiply: For multiplication of two numbers
• division: For division of two numbers

And at last, we export the Calculator Class through the module.exports

// ***** calculator.js file *****
class Calculator {
    
    // Constructor to create object of the class
    Calculator() {
        
    }

    // Prefix increment operation
    preIncrement(a) {
        return ++a;
    }

    // Postfix increment operation
    postIncrement(a) {
        return a++;
    }

    // Prefix decrement operation
    preDecrement(a) {
        return --a;
    }

    // Postfix decrement operation
    postDecrement(a) {
        return a--;
    }

    // Addition of two numbers
    add(a, b) {
        return a + b;
    }

    // Subtraction of two numbers
    subtract(a, b) {
        return a - b;
    }

    // Division of two numbers
    divide(a, b) {
        return a / b;
    }

    // Multiplication of two numbers
    multiply(a, b){
        return a * b;
    }
}

// Exporting Calculator as attaching
// it to the module object
module.exports= Calculator;

Step 3: Now let's code the "app.js" file. 

First, we will import the Calculator class by requiring it from the "calculator.js" file. Then we create an object  "calc" of Calculator class to use its member methods. 

// ***** app.js file  ******
// Importing Calculator class
const Calculator = require('./calculator.js');

// Creating object of calculator class
const calc = new Calculator();

/* Using all the member methods 
defined in Calculator */

console.log(calc.preIncrement(5))

console.log(calc.postIncrement(5))

console.log(calc.preDecrement(6))

console.log(calc.postDecrement(6))

console.log(calc.add(5, 6))

console.log(calc.subtract(5, 6))

console.log(calc.divide(5, 6))

console.log(calc.multiply(5, 6))

Step to run the application: Open the terminal and type the following command.

node app.js

In this way, you can use module.exports in node.js. In place of class here you can pass any variable, literal, function, or object. And later import it by using require()