Saving Changes to .scss and .js Project Files Doesn’t Trigger Parcel’s HMR: A Comprehensive Guide to Troubleshooting and Fixing

Are you tired of manually reloading your application every time you make changes to your .scss and .js project files? Do you expect Parcel’s Hot Module Replacement (HMR) to automatically refresh your application, but it just doesn’t seem to work? You’re not alone! In this article, we’ll delve into the possible reasons why saving changes to your project files doesn’t trigger Parcel’s HMR and provide you with step-by-step instructions to troubleshoot and fix the issue.

Understanding Parcel’s HMR

Before we dive into the troubleshooting process, let’s take a quick look at what Parcel’s HMR is and how it’s supposed to work. HMR is a feature that allows you to see the changes you make to your code in real-time, without requiring a full page reload. When you save changes to your project files, Parcel’s HMR is supposed to automatically reload the affected modules, injecting the new code into the running application.

How HMR Works

Here’s a high-level overview of how HMR works:

1. Parcel watches your project files for changes.
2. When a change is detected, Parcel rebuilds the affected modules.
3. The rebuilt modules are then sent to the browser via WebSockets.
4. The browser updates the application by injecting the new code.

Troubleshooting Steps

Now that we’ve covered the basics of HMR, let’s go through a series of troubleshooting steps to identify and fix the issue.

Step 1: Check Your Parcel Configuration

The first step is to verify that you’ve configured Parcel correctly. Check your `parcel.config.js` file and make sure it includes the following:

module.exports = {
  // ...
  hmr: true,
  // ...
};

If you don’t have a `parcel.config.js` file, you can create one and add the above configuration. This tells Parcel to enable HMR.

Step 2: Verify Folder Watching

Next, ensure that Parcel is watching your project files correctly. Check your `package.json` file and look for the following script:

"scripts": {
  "dev": "parcel watch src/index.html"
},

In this example, Parcel is watching the `src` folder for changes. Make sure the script points to the correct folder that contains your .scss and .js project files.

Step 3: Check Your File Extensions

Parcel only watches files with specific extensions. Make sure your project files have the correct extensions:

• .scss for Sass files
• .js for JavaScript files

If you’re using other file extensions, you may need to add them to your Parcel configuration. For example, to watch .css files, you can add the following to your `parcel.config.js` file:

module.exports = {
  // ...
  extensions: ['.scss', '.css', '.js'],
  // ...
};

Step 4: Verify WebSocket Connection

Parcel uses WebSockets to communicate with the browser. Check your browser’s console for any WebSocket-related errors. If you see an error, it may indicate a problem with your WebSocket connection.

Step 5: Check for Conflicting Plugins

Some plugins may interfere with Parcel’s HMR. Check your `package.json` file and look for any plugins that might be causing conflicts. For example, if you’re using `parcel-plugin-sass` and `sass-loader`, try removing one of them to see if it resolves the issue.

Step 6: Verify Browser Extensions

If you’re using browser extensions like React DevTools or Vue DevTools, try disabling them to see if they’re interfering with HMR.

Common Issues and Fixes

Here are some common issues and their fixes:

Issue	Fix
Parcel not watching changes to .scss files	Ensure you have the `sass` package installed and configured correctly.
Parcel not rebuilding modules when changes are detected	Check your `parcel.config.js` file and ensure the `hmr` option is set to `true`.
WebSocket connection errors	Check your browser’s console for any WebSocket-related errors and ensure your WebSocket connection is stable.

Conclusion

Saving changes to your .scss and .js project files should trigger Parcel’s HMR, allowing you to see the changes in real-time. By following the troubleshooting steps outlined in this article, you should be able to identify and fix the issue. Remember to check your Parcel configuration, verify folder watching, and ensure your file extensions are correct. If you’re still experiencing issues, try checking for conflicting plugins, browser extensions, and WebSocket connection errors.

With these steps, you should be able to get Parcel’s HMR up and running, making your development workflow more efficient and enjoyable.

Frequently Asked Questions

• Q: What if I’m using a different build tool, like Webpack?

  A: While this article focuses on Parcel, the troubleshooting steps can be adapted to other build tools like Webpack. The key is to understand how each tool’s HMR works and configure it correctly.

• Q: Can I use HMR with other frameworks, like React or Vue?

  A: Yes! HMR is framework-agnostic, meaning it can be used with various frameworks like React, Vue, or Angular.

Additional Resources

For more information on Parcel and HMR, check out the following resources:

• Parcel’s Official Documentation
• Parcel’s GitHub Issues Page

By following the steps outlined in this article and referring to the additional resources provided, you should be able to troubleshoot and fix the issue of saving changes to your .scss and .js project files not triggering Parcel’s HMR.

Frequently Asked Question

Got stuck with saving changes to .scss and .js project files not triggering Parcel’s HMR? Worry not, we’ve got the answers!