Develop Reference

Fundamental Understanding of Node JS in the front end

Some things to know:
I understand how to make a HTML / CSS / JS website.
I understand how to make a Node JS app and host it on Heroku
I encountered a problem that was very confusing and I still working it out. I am making a firebase project using their latest tree-shaking V9 SDK
import { initializeApp } from 'firebase/app';
I understand Node JS is meant for backend (it can't be run in a browser) so how am I supposed to "build" this into something that I can reference in a script tag? I've heard of webpack but that requires you to run npm run build so how is that practical in any way? That would mean every change I make I would have to build it?
Developer Testing:
How would one live preview this Node JS app on a localhost if Node JS can't be run in a browser? I would live to be able to preview this Node JS app and quickly make changes if that's possible.

I've heard of webpack but that requires you to run npm run build so how is that practical in any way? That would mean every change I make I would have to build it?
Yes, that's the general idea. You make changes to script files on your local machine (or network), and then in order to see the changes take effect, you rebuild the app so that a new bundle is generated. This bundle can then be hosted on your web server or development server, and once it's there, you can refresh the page to see the differences.
But almost all of this can be automated, resulting in it not really being much of a chore at all.
Nodemon is a popular tool that watches a directory for changes and can run Node scripts when a change is detected. With it, you could, for example, make a change to a file, and then it'll automatically rebuild your app.
For Webpack in particular, there's webpack-dev-server, which can automatically refresh a page when the app gets rebuilt.
So, during development, the workflow can be as simple as - make a change, then alt-tab to your browser (hosting the app on localhost) to look at the changes.
Bundles built for the purpose of eventually hosting them on the front-end can easily incorporate Node modules - the build process can take the code from the module, and the bundle produced can include that code. This sort of thing is extraordinarily common.

Why JavaScript frontend framework is needed for Node.js to run?

When we talk about JavaScript vanilla it's frontend programming language; It needs a webserver like IIS, Apache or nginx etc to deliver the content to a client when requested. After that, JavaScript runs on client browser, but every video or article I found said we need to install node.js to make this work. What I know about node.js is its a runtime environment to make JavaScript work outside the browser; like for a backend api or regular desktop application.
Here is my question:
Why do we need to use Node.js if our target is to deploy a frontend webapp that's gonna run on the client browser?

You don't have to install and use Node to make frontend applications, but it can help a lot, especially in large projects. The main reason it's used is so that script-writers can easily install, use, and update external packages via NPM. For a few examples:
Webpack, to consolidate multiple script files into a single one for production (and to minify, if desired)
Babel, to automatically transpile scripts written in modern syntax down to ES6 or ES5
A linter like ESLint to avoid accidental bugs and enforce a consistent code style
A CSS preprocessor for Sass that can turn (concise) Sass into standard (more verbose) CSS consumable by browsers
And so on. Organizing an environment for these sorts of things would be very difficult without NPM (which depends on Node).
None if it is necessary, but many find that it can make the development process much easier.
In the process of creating files for the client to consume, if you want to do anything more elaborate than write plain raw .js, .html, .css files, you'll need something extra - which is most often done via NPM.

It's only for extra support during development, and ease of installing libraries. almost like an extra IDE / helpful editor
for example you might want to see changes you make on your HTML and frontend javascript code, without having to refresh the preview browser. node will provide a package that does that...
it also helps install and use libraries easier. for example, if you want to add a library like bootstrap to your frontend, rather than searching around and downloading the files... but if you use node project, you can simply use npm install bootstrap that will automatically download the lastest version from the right source.
that's all

Bundle and publish client-side web code on NPM

I made a Javascript file. Let's say the contents of it are this:
let myCoolAlert = (str) => {
alert(str)
}
// in a different js file (SO doesn't allow you to cross-file as far as I know
myCoolAlert('Hello World!')
I already hosted the JS file on a CDN. Now, I want it to be automatically hosted locally by whoever installed it if you install it via NPM. Is there a way to do this?
Also, I noticed that to do the same using Socket.io, you have to pass Socket.io to the HTTP/HTTPS server you created. Will I have to do this also? (I would prefer not).
Thanks!
Edit:
I am trying to make a better alert system (like sweetalert). I coded it in Javascript and works when using it through the CDN. However, I also want users to be able to install this via NPM (kind of like SweetAlert? I am not sure about that last statement however because I do not use it). When they install it with NPM, it's obviously going to be useless because it is for the browser. However, I want them to either:
Automatically have the source code needed available at a URL like localhost:3000(or server name)/betterAlert.js and be able to use that URL as a script in the HTML files
OR, have the user pass the HTTP or HTTPS server they created to the module (like socket.io does) and have it automatically host it from there.
Please note:
The code I am trying to bundle is native to the web. Will it still work with a bundler like webpack?
Is this possible? Thanks again.

To bundle client-side code and publish it through NPM you'll need to do a couple things: learn how to package and publish modules, and write some code that can be consumed. This means using module.exports or export to expose your library, depending on whether you want to use CJS or ESM. The consumer of your library can usually be assumed to be using Webpack, Fuse, Rollup, or some other bundler which knows how to deal with modules.
You can also use a tool like Rollup yourself to build and bundle up your library for different targets and apply various transformations to it (example from my own library boilerplate). Using a bundler like this makes more and more sense as your library inevitably grows larger.
Using modules like this rather than distributing through a CDN or in some other way that puts your library code on the global/window object is generally better for consumption in complex apps, large apps, and/or apps already being built with tools like Webpack (so, anything written in React, Angular, Vue, etc.). But having a CDN distribution is still a good idea for something like your library, since it may well be used by people building sites with jQuery and vanilla JS.

hooking into Google App Engine's deploy

The Google App Engine Launcher has a nice little "Deploy" button that will push my changes to prod. However, I'd like to be able to minify/obfuscate my JavaScript before deploying.
I've read about several tools that can do this: Google Closure Compiler, Uglify.js, YUI Compressor. Of course, I could do this manually before deploying, but I'd much rather be able to have this run automatically.
Is there a way to hook into App Engine's deploy process, and run a minification/obfuscation task on my JavaScript? If not, any suggestions on other approaches?

As already mentioned minifying and obfuscating the code depends on the specific setup of your app and has to be done before deploying on App Engine.
That was one of the main reasons that I started the gae-init project. Among other things it has a custom script that combines and minifies all the static files (JS/CSS) before deploying, while when running locally keeping them as they are.

Not sure if there's a way to hook to "App Engine Launcher" but all it does is run a appcfg.py update myapp/ command where myapp/ is your app directory. You could simply create your own shell/batch file where you first minify the files and then deploy them by running the command above.
Also, take a look at Google's Pagespeed service that comes with paid App Engine projects where css/js/etc is minified automatically on Google's servers.

How to use New Relic with ember-cli?

right now I'm running an ember-cli application on heroku by serving it with the ember server command (not sure if this is the best method) and I'd like to integrate it with New Relic, but I have no idea how to do it.

Careful, ember server starts a live-reload server for development purposes — you edit a file, save it, and the application gets rebuild in an instant — you should not use it to serve an Ember app in production, it's a potential security risk. Normally you run ember server only on your local computer where you develop the code.
For production, build your app with ember build --environment=production, that will create a set of static files in your project's dist/ directory. You can upload these as you would upload any HTML/CSS/Javascript.
Keep in mind that Ember (and other frameworks of this kind like Angular and Backbone) is a single page application (SPA) framework; there is no server-side code at all, it all runs in the browser. Usually you would provide some sort of API (like a REST-API) on the server to provide and process data from a database or to provide other server-side services. That way you can develop the front and back-end separately.
I'm not too familiar with New Relic, but as far as I can tell it is analytics software that runs on the back-end, so it has nothing to do with your browser-side framework.

At the server folder, just find the index.js file and add require('newrelic'); at the beginning of the file. Of course you should also follow the instructions when you setup New Relic at you Heroku App, setting your application as a node.js app, which means you'll have to run npm install --save newrelic, go to your node_modules folder, find newrelic, copy newrelic.js file to the root of your application and edit the file with your app_name and license_key.

I recently removed my code from <meta ... in app/index.html and started to use this addon Ember-new-relic.

Get the JavaScript snippet.
And add it below <meta http-equiv="X-UA-Compatible"... in app/index.html.