Import Export

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To make objects, functions, classes or variables available to the outside world, simply export them and then import them into other project files where necessary.

"Hello, World!" on Node.js

Node.js® is a JavaScript environment built on the Chrome V8 engine.

Let's get started with Node.js just by typing node in the console:

$ node
>

If you don't have it, then download and install it on your computer.

Now let's try to print something:

$ node
> console.log('hello from Node.js')
// After hitting Enter, you get this:
hello from Node.js
undefined

Export

Feel free to experiment with Node.js using this interface: it is common to test small pieces of code here if it is not practical to put them directly into a file.

It's time to create our Hello Node.js application!

Let's start by creating the index.js file. With the next command we create the folder myProject and enter it.

mkdir myProject && cd myProject

Now we create the index.js file itself

touch index.js

Open your code editor or download and install it. We recommend VS Code.

Open the code editor and add the folder of the project we created to it.

new prroject

Now open the side menu by clicking this icon.

new prroject

Copy the following piece of code into it:

// index.js
console.log('hello from Node.js')

To run this file, you must reopen your terminal and navigate to the directory where index.js is located.

In VS Code this can be done by clicking on these icons.

new prroject

And choose the tab TERMINAL

new prroject

Once you have successfully navigated to the desired location, run the file using the command

node index.js

You will see that this command will produce the same output as before, printing the string directly to the terminal.

new prroject

Application modularity

Export

It's time to move to the next level! Let's create something a little more complex by splitting our source code into multiple JavaScript files for the sake of readability and maintainability.

Project structure

Create the following directory structure (with empty files), but don't create package.json yet, we will generate it automatically in the next step:

├── app
|   ├── calc.js
|   └── index.js
├── index.js
└── package.json

To create a new file or folder in VS Code click the corresponding icon as shown in the picture.

new file

package.json

Every Node.js project starts by creating a package.json file. You can think of it as a JSON representation of the application and its dependencies. It contains the name of your application, the author (you), and any dependencies required to run the application. This is your project map.

You can interactively generate the package.json file with the command

npm

npm init

in the terminal. After running the command, you will be asked to enter some information, such as your application name, version, description, and so on. No need to worry, just press Enter until you get the generated JSON and the question is is it ok ?. Press Enter one last time and voila: your package.json has been automatically generated and placed in your application folder. If you open this file in your IDE, it looks very similar to the code snippet below.

// package.json
{
  "name": "myproject",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "ISC"
}

It is good practice to add a startup script to your package.json package. So add the following line to the scripts object:

"scripts": {
  "start": "node index.js", // this line
  "test": "echo \"Error: no test specified\" && exit 1"
}

Once you have done this, you can start the application with the npm start command.

Import

Now let's go back to the first file you created called index.js. It is recommended to keep this file very compact: only include the application itself (the index.js file from the / app subdirectory created earlier). Copy the following code into your index.js file and save:

// index.js
require('./app/index')

or shorthand for all index.js files

// index.js
require('./app')

If a specific file is not specified, then the code interpreter looks for the index.js file and enters it. This is how we simply connected our first file to the project.

Export

Now it's time to start building a real application. Open the index.js file from the /app folder to create a very simple example: adding an array of numbers. In this case, the index.js file will only contain the numbers that we want to add, and the logic that requires the calculations must be placed in a separate module in the calc.js file. Paste this code into the index.js file in the /app directory.

// app/index.js
const calc = require('./calc')
const numbersToAdd = [3, 4, 10, 2]
const result = calc.sum(numbersToAdd)

console.log(`The result is: ${result}`)

Now paste the actual business logic into the calc.js file that can be found in the same folder.

// app/calc.js
const sum = arr => {
  return arr.reduce((a, b) => a + b, 0)
}

module.exports.sum = sum // export

In this file, we created a sum function and exported it, made it available in other files in the project.

To check if you did everything right, save these files, open a terminal and type npm start or node index.js. If you did everything correctly, you will receive the answer: 19. If something went wrong, carefully review the log in the console and find the problem based on it.

new file