Intro to Node Node's Built-in Modules

Learning objective: By the end of this lesson, students will understand the concept of modules by learning how to require and use core Node modules, such as fs, in their applications.

Node’s built-in modules

In the broad context of programming, a module is a reusable block of code. In Node specifically, a module refers to a JavaScript file that can be easily used in other JavaScript files, allowing for code reuse and modular programming.

Think of modules as the rooms in a house, where each room serves a specific purpose. In a home, the kitchen is used for cooking meals. A living room offers space for relaxation and entertainment. A garage provides a place to store a vehicle.

Each module in Node, like a room in a house, is designed for a particular set of tasks, making the overall structure of an application functional and organized. Like you wouldn’t cook a meal in your bathroom, you won’t use the same module to handle user events and connect to a database.

📚 A module is a self-contained unit of code that encapsulates a specific functionality, which can be easily used in other parts of a program.

Core modules in Node

Node has a set of built-in core modules, each designed for specific functionalities. Among these are:

• http: Enables the creation and handling of a web server.
• fs: Provides the capability to read from and write to the file system.

A comprehensive list of Node core modules is available here.

The importance of documentation

Before using any module, familiarizing yourself with its documentation is crucial. For example, the fs module’s documentation details various methods to interact with the file system.

Understanding writeFile()

One of the methods, writeFile(), is used for creating files. It requires three parameters:

• file: A string specifying the file’s name.
• data: The content to be written to the file.
• callback: A function that executes after the file is created.

Additionally, there’s an options parameter, which is optional. This is communicated in the documentation by being enclosed in square brackets as shown here: fs.writeFile(file, data[, options], callback). Using square brackets to indicate optional parameters is a common pattern in JavaScript documentation.

Implementing writeFile()

Let’s put this into practice. In your server.js file, write:

const fs = require('fs');

fs.writeFile('./hello.txt', 'hello, friend', () => {
  console.log('done creating file');
});

What’s happening in the code

• Requiring the fs module: The fs module is required, making its functionality accessible.
• Using writeFile(): We utilize writeFile() to create a hello.txt file and write the text hello, friend into it.
• Callback function: A callback function logs a message to the console upon file creation.

This callback function in Node is conceptually similar to callbacks in browser event handling. However, here, it responds to a new type of event - the end of the file creation process.