Building a Node.js Application with Reactive Programming
Reactive programming is a paradigm that allows us to write more efficient and scalable code. In this article, we’ll explore how to build a Node.js application using reactive programming with RxJS.
The Problem with Manual Restarting
Manually restarting an application’s process after each change to the codebase can be frustrating and time-consuming. Fortunately, there’s a solution: Nodemon. Nodemon watches for changes in a given directory and restarts our app after each one, allowing us to focus on writing code.
How Nodemon Works
Nodemon uses the FSWatcher API to watch for changes in the file system. However, this API has some limitations, such as notifying us twice for each change. To overcome this, we can use a package called chokidar, which provides a more reliable way of watching for changes.
Building Our Application
We’ll use RxJS as the core library for our application. RxJS makes it easy to work with event-based architecture and provides a lot of useful operators for managing streams of data.
Command Line Usage
We want our app to be accessible like a command in our console. To achieve this, we’ll use a package called commander, which allows us to parse arguments and create a command-line interface.
Implementation
First, we’ll get and parse the arguments passed to our script. We’ll use the process.argv variable to access the arguments and the commander package to parse them.
Next, we’ll set up a listener for changes in the file system using chokidar. We’ll use the fromEvent function from RxJS to create an observable that listens for changes.
Filtering and Debouncing
We’ll use the filter operator to filter out changes that don’t interest us. We’ll also use the debounce operator to delay the execution of our script by a certain amount of time.
Displaying Messages and Executing Scripts
We’ll use a helper function to display messages and execute scripts. We’ll use the spawn function from the child_process module to execute commands.
Putting it all Together
Here’s the complete code for our application:
“`javascript
const { fromEvent } = require(‘rxjs’);
const { filter, debounce } = require(‘rxjs/operators’);
const chokidar = require(‘chokidar’);
const commander = require(‘commander’);
const childProcess = require(‘child_process’);
// Get and parse arguments
const args = commander.parse(process.argv);
// Set up listener for changes
const watcher = chokidar.watch(‘.’, {
persistent: true,
ignoreInitial: true,
});
const changes$ = fromEvent(watcher, ‘change’);
// Filter and debounce changes
const filteredChanges$ = changes$.pipe(
filter((path) => path.endsWith(‘.js’)),
debounce(1000),
);
// Display messages and execute scripts
filteredChanges$.subscribe((path) => {
console.log(Changed file: ${path});
const script = childProcess.spawn(‘node’, [path]);
script.stdout.pipe(process.stdout);
script.stderr.pipe(process.stderr);
});
“`
Conclusion
In this article, we’ve built a Node.js application using reactive programming with RxJS. We’ve used the FSWatcher API and the chokidar package to watch for changes in the file system and the commander package to parse arguments and create a command-line interface. We’ve also used the filter and debounce operators to manage the stream of changes and display messages and execute scripts.