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Next.JS unused javascript slow performance

I am doing my first website with Next.Js and after I do the lighthouse test I get really bad performance score. It says it is for unused JavaScript. Those files are in the chunk folder. I read a lot that I should split that code in order to make the page faster, but I couldn.t find a anything about how to do it. If there is someone that knows about it, it would be a great help. Below is a screenshot of the lighthouse:

Delete all chunks and generated code, then do a production build using npm run build instead of npm run dev when you're running it on a live server.

Organising a client & server SPA/Node.js application

I am writing an application with a Node.js backend and a single-page web app front-end.
I am keeping the client and server logic in the same project for simplicity and speed of development.
I am considering how best to organise the artifacts.
The Node.js part is straightforward because it doesn't need to go through a battery of pre-processors (transpilation, minification, concatenation etc).
The front-end needs to be transformed per the above, and I guess placed in a dist folder.
The current hierarchy of files is like so:
my-app
- src
- client
- server
Should I put the dist folder for the client artifacts under src/client?
Has anyone tried this and found problems with this approach?
I am using Heroku (a deployment system that uses git).
Committing the built artifacts for the client feels wrong, but if I want to deploy it by pushing to Heroku I think I need to commit them. Is this correct?

This question, as is, invites opinionated answers, so I'll start by saying this is by no means the only way to go, but in my opinion, it is the easiest to work with and makes the most sense.
The production client code, after pre-processing, should be located in my-app/dist or my-app/dst, which could either mean distribution or destination, depending on how you look at it. Either way, my recommendation is to commit this folder, as it saves you a lot of hassle debugging remotely.
For example, if your code works locally but not remotely, using something like the postinstall hook to generate your dist folder adds yet another suspect to check when trying to determine what the issue is with your program.
Another advantage of committing the dist folder is it allows you to specify all the packages you use for your build process as devDependencies rather than dependencies. This is a huge plus, and makes deployment a lot faster, as well as less memory usage on your heroku process.
That being said, I still recommend (as you already probably plan to do) using an automated watch task to build your dist folder for ease of development, even if you decide you don't want to use that same build process remotely and opt for committing the dist directory instead. You could add that as a custom npm command, e.g. npm run build and have that invoke your gulp task.
One last thing. For those of you using templating languages like pug or dust or ejs instead of a framework like react or angular, I recommend determining whether you can run any of your templates to build static HTML files that will be served in production.
If not, you should at least compile your templates (not to be confused with running them) by following the recommendations provided by your particular templating language. Typically, they'll suggest using their command line utility to generate the compiled templates, so that they don't have to be compiled every time they're invoked in production. This will make your node.js server respond faster to requests at the expense of using more memory to cache the compiled templates.

If you're planning to go this route, I would edit nodejs app.js/index.js to serve static file and point the directory to dist/.
Also, you would need to tell express to forward all non-api requests to the frontend.

Version control strategy for webpack-encore project

I'm learning to use webpack-encore and noticed it is installed only as a dev dependency. Does that mean I should compile my js and css files on development and push them to the repository, and then to production?
That seems to me what the docs are implying, but wouldn't that mean a merge-conflict hell? Compiled files would be impossible to merge.
Also wouldn't that be contrary to version control philosophy? As far as I know, you don't publish binaries in compiled languages (i.e. C/C++), you push the code and expect the server to compile them. I know this isn't the same type of "compilation" in javascript, but what is the expected behavior of the production server in this case? To receive the files ready to serve them, or to compile them at the time of release?
Thanks in advance

Does that mean I should compile my js and css files on development and push them to the repository, and then to production?
Not exactly - it depends on how you deploy.
When you deploy, you need to run ./node_modules/.bin/encore production to build your assets. Once you've done this, only your built assets (e.g. web/build) need to be transferred to production.
You could run this command locally (or on some "build" server) and the transfer all the files to production. Or, you could use a git pull on production, and then run this command on production (the downside being that you would need Node.js installed on production).
You shouldn't / don't need to commit your built files to your repository. But... if it simplifies your deploy (i.e. you want to do a git pull and be done), there's no real problem with that.
I just added a PR to answer these in the FAQ (http://symfony.com/doc/current/frontend/encore/faq.html) - here's the PR until it's deployed: https://github.com/symfony/symfony-docs/pull/8109
Cheers!

Solution 1:
Run yarn run encore production locally
Check out which files have been created / modified
Add them to VCS
Commit
Push / deploy
Solution 2:
Push / deploy
Run yarn run encore production remotely during deployment
To my eyes the 2nd solution is way better, because you don't need an extra human-checking before deployment, everything is automated.
But this has a strong drawback: building assets can be a slow process, and when I deploy, my production is down during 5 to 20 seconds until assets are built.
Here's the HTTP 500 error:
An exception has been thrown during the rendering of a template ("Asset manifest file "[...]/web/build/manifest.json" does not exist.").
It looks like the manifest.json file is deleted at the beginning of the process, and created from scratch later on.
Something that should be improved?

What is "npm run build" in create-react-app?

I could not find any explanation regarding the work of "npm run build",
It is simple and easy to use and i get the "build" folder that works great,
But, in create-react-app, what happens exactly behind the scene?
Is it a complete different use of a build tool?
If not, is it utilizing other build tools?

Developers often break JavaScript and CSS out into separate files. Separate files let you focus on writing more modular chunks of code that do one single thing. Files that do one thing decrease your cognitive load as maintaining them is a quite cumbersome task.
What happens exactly behind the scene?
When it’s time to move your app to production, having multiple JavaScript or CSS files isn’t ideal. When a user visits your site, each of your files will require an additional HTTP request, making your site slower to load.
So to remedy this, you can create a “build” of our app, which merges all your CSS files into one file, and does the same with your JavaScript. This way, you minimize the number and size of files the user gets. To create this “build”, you use a “build tool”. Hence the use of npm run build.
As you have rightly mentioned that running the command (npm run build) creates you a build directory. Now suppose you have a bunch of CSS and JS files in your app:
css/
mpp.css
design.css
visuals.css
...
js/
service.js
validator.js
container.js
...
After you run npm run build your build directory will be:
build/
static/
css/
main.css
js/
main.js
Now your app has very few files. The app is still the same but got compacted to a small package called build.
Final Verdict:
You might wonder why a build is even worth it, if all it does is save your users a few milliseconds of load time. Well, if you’re making a site just for yourself or a few other people, you don’t have to bother with this. Generating a build of your project is only necessary for high traffic sites (or sites that you hope will be high traffic soon).
If you’re just learning development, or only making sites with very low traffic, generating a build might not be worth your time.

It's briefly explained here: https://github.com/facebookincubator/create-react-app#npm-run-build-or-yarn-build.
It correctly bundles React in production mode and optimizes the build for the best performance.
The build is minified and the filenames include the hashes.
Behind the scenes, it uses babel to transpile your code and webpack as the build tool to bundle up your application.

How make deployment onto Amazon Web Services (AWS) with ReactJS/NodeJS together?

I currently have ReactJS + NodeJS/ExpressJS + Webpack onto EC2, Amazon Web Services (AWS) under one project and would like to get it deployed together at once, in one project.
What are some suggestions on how to go about doing so? Done the research, and I've only seen tutorials on deploying one in specific, whether it be just ReactJS or just NodeJS. Any insights or leads would be greatly appreciated.
Will accept/upvote answer. Thank you in advance

You don't "deploy" ReactJS, it's just a static file or files like any other JS libraries in your applications. You also don't deploy Webpack. Webpack should run on a developer machine (or in CI/CD stack or build system).
As for the NodeJS part just use Elastic Beanstalk.

I do not commit builds to source control. I see that a lot and it can make things easier, but you can also forget to rebuild as you have to do it manually, and it adds a lot of bloat to your repo.
I believe builds should be run as part of the deployment process. Assuming you are using git, you can add script hooks/post-receive in a remote repo there. When you push to that remote, the script will run. This is where I do my webpack build.
You may want to look into https://github.com/git-deploy/git-deploy for context, but I do this manually.
In my projects, on the deployment machine I do git --init --bare /var/git/myproject.git then add the script in /var/git/hooks/post-receive. The hook checks out the code into /var/www/myproject, runs the build, which fills in the /var/www/myproject/build. Then it removes the old /var/www/myproject/public and renames build to public. And done.

I'm coming from more of an operations background and would say that if your goal includes keeping that site up as much as possible then use Packer to generate AMI's and CloudFormation to build an Application Load Balancer (the newer, cheaper brother of ELB) in front of an AutoScalingGroup which keeps the EC2 instances up and running.

I'm currently working on a large scale project doing exactly what you describe. First off, there are so many different ways to do this, so what you really need is some general guidelines to get started, then we can dig a little deeper into details when some initial decisions are made, if you'd like. If you've already got the app deploying and running in two separate steps, but are just looking to combine those, I can definitely help. I'd just need to know how you're currently building/deploying. If you're just getting started on building your pipeline and need to set up the process from scratch, then read on:
First off you'll want to set up some kind of build server that will install your npm dependancies and run your webpack build. Most likely you'll want a separate webpack config that's just for your build server, this'll give you a build optimized for production or qa/staging environments. This config should split out vendor files that you won't update all the time, pull out seperate css files with extract text plugin and uglify the files. If you have an isomorphic React app, or are using es6 features not supported in your version of node, then you'll need a webpack build for your server code as well. This is really different from the hot reloading build you'll want to have on your local machine while you're actually coding the app. I'll be happy to show some examples if you'd like of our webpack config files for both local development and our CI build. You may also need a build.sh or makefile to do something with the compiled .js files that your webpack build creates, but that'll depend on your deployment which I'll cover later. You can run your production build locally as your getting your config just right and fire up the app from those files to test it's all working. Additionally, since you'll likely want to be able to automate all of this, you probably want to run your tests and linting right before you build your app, we run eslint and mocha/jdom to run our enzyme/expect specs as part of our build. Once that's all working nicely, you'll most likely want to set up a build server that can run your builds automatically. My team is using Jenkins for this, which is a little more work to set up, but it's free (aside from the ec2 box we run it on). There are also a ton of subscription based build/continuous integration servers, such as Travis and CodeShip. There's plenty of articles on the pros and cons of these different products and how to set them up. The bottom line is you'll want to have a build server that can pull down your code from source control, install npm deps, lint, test and build your app. If anything fails it should fail your build and if your build succeeds you'll have some sort of archive that you'll later deploy to an ec2 instance. In our shop we use a build.sh file to tarball up our build archive (basically a folder with our node server files as well as our minified client files, css files and any fonts or images needed to run the app) and upload it to an S3 bucket that we deploy from. We like this fairly old school method because the tarball will never change, so we have ultra reliable roll backs.
What you do with your build archive will depend on how you want to do deployments. We have a custom deployment system using puppet, but there are plenty of products that do this such as elastic beanstalk, that would be much easier to set up. You'll want some kind of process supervisor to actually run your node app, so unless you have a dev ops team that wants to build custom pipelines, using AWS built in features will probably be the easiest way to get started. As usual, there are so many ways to do this, but the basic principal is that you need something to download your build archive and run/supervise your node process. You also may want to be able to create and configure ec2 boxes on the fly (Puppet, chef, etc.), or even use containers (Docker) which allow you to move complete stacks around as single units. Using automation to create and configure servers is crucial if you need to scale your app, but it is complicated and may not be necessary for smaller projects. This is definitely an area where you can start simply and add complexity later on, as long as you have good long term goals and make sure to take the necessary step to prepare for future complexity.
All of this can get you pretty far in the weeds, so it's best to find the simplest thing that will serve your needs as you get started and then add complexity as real life situations demand so. I'll be happy to elaborate on any of these details if you provide a little more context about how big and well funded of a project your working on. If it's a little side project to learn the tech, I'd have very different advice then if you're trying to build an app that'll have a lot of traffic and/or complex features.

This could get 100 different answers and they could all end up being good ideas. First, you mention react + nodejs - keep in mind that these solve different tasks. React is going to be frontend and served out via static files. Nodejs is focused more around the server-side and would be the code that serves data. They can easily work together. You might use Express for the webserver (nodejs) to serve the HTML/React pages.
Unfortunately, I saw that you mentioned webpack, so you are going to have to 'build' your application with something - either via webpack, gulp, grunt, etc. This is where source control and build servers are great - but if you're new to it, it might be more complex than you need.
If you have just basic EC2 images as webservers and only 1-2, then the biggest hurdle is just pushing up your code. Something like https://deploybot.com/ could work as it can push your git repo down to multiple hosts via ftp, etc. If you wanted to get a bit fancier, you could look at something like Jenkins or some of the other items.
Docker is a great choice and if you are going to be dealing with multiple developers, server environments, deployments - it's worth the time. Otherwise, keep it simple and just get your code on the EC2 instance ;).