Develop Reference

how to change the code of other modules in nodejs

For example.I installed a module in the node_modules. if i change that module, updating node_module will update all modules.What is the usual practice

Look into patch-package
In summary, you install the package and add a postinstall script to your package.json file that calls patch-package:
"scripts": {
"postinstall": "patch-package"
}
Modify the package directly in /node_modules and then call patch-package on the package you just modified:
npx patch-package <package_name>
This will create a local directory called /patches with a diff (or patch) file inside for that package. Commit that folder in with your repo.
Now whenever you run npm install, the postinstall script will also run and apply the /patches that you committed to that package 🙌🏽

First, We call it Package instead of Module, Why? because search results on Google are much more accurate when you use that word
Second, to update a specific package use npm update {package name}
Third, you don't change the code of other packages, you can only either install, update, or delete the package. there's this option to override it but it's only possible if the package owner allows overrides.
Update
I decided to update my answer due to the discussion below.
since I have put in mind that you are a beginner and are not entirely sure how to update code or override package code, or maybe even if it's a good idea to change package code, I have given you an unclear answer.
and since the other answer are telling you to use patch-package
then I'm here to tell you that you can fork that package. and install that package from your fork. here's how you do it

how to use yarn to install swal

I'm new to yarn.
So I've my rails 5.1 application with yarn, I want to add this package:
https://yarnpkg.com/en/package/swal
So I do:
yarn add swal
it got added to node-modules/swal a lot of files but not the js that I should require.
I go to that folder and do npm install.
but I still dont have my swal.js to include...
I read the README and it says to run npm run build, it throws a dependency with vue error.
So I start to wonder.. I 've to investigate how to build each JS? Is that better than just get the .js already compiled and put it on vendor folder?
Anyway my question here is concrete, what is the way to add swal.

How do I use JSDoc on Windows?

Forgive me if this is a daft question but I'm utterly baffled as to how I can use JSDoc on Windows. I'm aware of JSDoc-Toolkit but it's a bit out of date and the google code repository recommends to use JSDoc 3 instead. I have downloaded JSDoc from Github and unzipped the jsdoc-master folder onto my local disk but can't find any solid information as to how to use it to parse my files.

You can download it as an npm package for the Node.js JavaScript runtime environment.
Install Node.js which comes with npm
Open your a command line
Install JsDoc by typing the following command
npm install -g jsdoc
Run JsDoc / generate documentation. more info
jsdoc path/to/file.js
Configure jsdoc (Optional)

The installation is not good documented on the project-page.
It is much better exlained on the github-page.

I don't know very much about NodeJS/npm ecosystem. However, I did the following steps below and it worked for me (on windows):
Downloaded NodeJS zip file and extracted, it made a directory 'node-v16.15.1-win-x64' with node.exe and and npm.cmd inside
Executed command 'npm install -g jsdoc', under the 'node_modules' directory under the 'node-v16.15.1-win-x64' it installed the jsdoc (in a folder) and also made the jsdoc.cmd file inside 'node-v16.15.1-win-x64'.
This jsdoc.cmd works with the full path but it does not work without the full path
jsdoc gets installed and is working with the above steps but to access it from any where without giving the full path, I had to set the 'node-v16.15.1-win-x64' on Windows PATH, that works.
I am not sure if question of OP is answered but JSDoc works for me this way.

I'm not saying this is necessarily the best way, but it worked for me:
Install node.js
Open a command prompt
As a test, create a folder in your root drive (c:\test) and go to it (cd\test). I guess there was some sort of permission issue as I couldn't get the following steps to work in my desktop folder.
Install the JSDoc package: npm install jsdoc
There should be a folder in test called node_modules
Go to the .bin subfolder in node_modules
There should be a file called jsdoc.cmd. Simple use jsdoc myfile.js in the command prompt to execute the JSDoc script on your file

Node.js project with no package.json

Is it ok to have a node.js project with no package.json? The ones I see on the internet all come with package.json
What is the effect of having no package.json?
How is package.json created in the first place? Is it created automatically? I am wondering why I do not have package.json

Fundamentally, package.json is a meta file for your application. It lists all the configuration of your application.
What is the effect of having no package.json?
Nothing as far as you're running all your code locally and have no requirement for deployment whatsoever.
Let's setup a scene for you to understand this better.
Imagine that you wrote a brilliant application using node. Now all the chicks in your surrounding want it to play with. It is so fantastic!
Now you want to give it to them and during the development process you `npm install`ed so many things that your project grows beyond 4TB size.
There is no data storage device available to ship that huge code base.
Then the girl of your dream said I want it and I want it now. So you begin searching for app deployment process for node applications.
That is where you stumble upon a magical thing called package.json.
So what you do is you list all your npm installed modules under dependencies property. Then you delete node_modulesfolder, add package.json and commit the entire damn thing in github. Even the .zip file is of 10MB
Then she gets the code.
Types in npm install && npm start (which will install all the dependencies from the package.json` and start your application)
If you have package.json however, that is where you specify all your dependencies.
Using --save flag of npm install
Example.
npm install express --save
How is package.json created in the first place? Is it created automatically?
You can manually create a text file and save it as package.json
OR
A more sophisticated way is to use the command
npm init
I am wondering why I do not have package.json
Me too! :)
You're most probably following a tutorial that doesn't emphasize on initial configuration of the project OR the author of those tutorials presume that the reader has all the fundamentals down to begin with.

It is created automatically if you write npm init.
Then, every package you add using npm install packagename --save will be added to the dependencies list.
You need package.json so that when you want to use your project on another machine you don't have to copy all node_modules, but only your .js files you have written, assets and package.json. You can then run npm install command and it will automatically download and install all the required modules (found in the list of dependencies inside package.json).
You can also manually create or edit it, but it's easier to add --save when installing a module so you don't have to worry about package versions and stuff like that.
Also if you want to create a npm package, an open source project or stuff other people will use, it's either required or the norm to have this package.json file describing your project.

package.json is npm file, if you don't use npm you will not have this file, npm is a great tool if you want to use external libraries in your project but if you don't need it (which is very not likely unless you are doing something very simple), you don't need package.json file too.
To generate package.json file initialize npm in your project using npm init

possible reason thus it exist is you maybe you enter a wrong command like npm i -y, you must initialize the project first, just enter a command npm init -y
Welcome.

Well, if you are running it on your local machine, it's fine. now to answer your last question, package.json is not created automatically.
the npm command npm init -y creates the 'package.json' file. It basically makes sharing your code and installing your codebase easier.

Change Directory in Node REPL not working?

Just earlier, I posted my question:
https://stackoverflow.com/questions/28336443/how-to-not-put-my-js-files-in-user-myuser-for-node-js
I have a file, hello.js, located in /Users/MyUser/Desktop/Node/
I can see that my default directory is /Users/MyUser/
Okay, so I get that I need to change my working directory. What I have been able to find so far is to use >process.chrdir('/Users/MyUser/Desktop/Node/');
Cool, that works, but now when I get out of the REPL shell, the directory resets.
The person who responded to my question said that I needed to run >node init and later npm install <name of dependency> --save
My first question: I have ran >node init and see that I can create this package.json file, what does this do exactly?
Secondly: I was told that I need to add dependancies. Could someone please explain to me what this means in Node terms? Does a dependancy simply mean a folder that I want node to include? Do I want to add this Node folder on my Desktop to be able to run my scripts?
I am currently trying to go through the learnyounode courses, however I do not want to have to save all of these test files in my /User/MyUser directory, so any advice would be greatly appreciated.
Thanks

I have ran >node init and see that I can create
this package.json file, what does this do exactly?
npm init is used to create a package.json file interactively. This will ask you a bunch of questions, and then write a package.json for you.
package.json is just a file that handle the project's dependencies and holds various metadata relevant to the project[ project description, version, license information etc]
I was told that I need to add dependencies. Could someone please
explain to me what this means in Node terms?
Lets say you're building an application that is dependent on a number of NPM modules, you can specify them in your package.json file this way:
"dependencies": {
"express": "2.3.12",
"jade": ">= 0.0.1",
"redis": "0.6.0"
}
Now doing npm install would install a package, and any packages that it depends on.
A package is:
a folder containing a program described by a package.json file
a gzipped tarball containing (1)
a url that resolves to (2)
a # that is published on the registry with (3)
a # that points to (4)
a that has a "latest" tag satisfying (5)
a that resolves to (2)
If you need to install a dependency that haven't been included in package.json, simply do npm install <packageName>. Whether or not you want to include this newly installed package in package.json is completely your take. You can also decide how this newly installed package shall appear in your package.json
npm install <packageName> [--save|--save-dev|--save-optional]:
--save: Package will appear in your dependencies.
--save-dev: Package will appear in your devDependencies.
--save-optional: Package will appear in your optionalDependencies.
Does a dependency simply mean a folder that I want node to include?
Umm, partly yes. You may consider dependencies as folders, typically stored in node_modules directory.
Do I want to add this Node folder on my Desktop to be able to run my
scripts?
No, node manages it all. npm install will automatically create node_modules directory and you can refer to those dependencies with
require() in your .js files
var express = require('express');
Node REPL simply provides a way to interactively run JavaScript and see the results. It can be used for debugging, testing, or just trying things out.
process.cwd() points to the directory from which REPL itself has been initiated. You may change it using process.chdir('/path'), but once you close the REPL session and restart, it would always re-instantiate process.cwd() to the directory from which it has been started.
If you are installing some packages/dependencies in node project1 and think those dependencies can also be useful for node project2,
install them again for project2 (to get independentnode_modules directory)
install them globally [using -g flag]. see this
reference packages in project2 as
var referencedDependency = require('/home/User/project1/node_modules/<dependency>')
Simply doing process.chdir('/home/User/project1/node_modules/') in REPL and referencing as
var referencedDependency = require('<dependency>') in your js file wont work.
>process.chdir('/Users/MyUser/Desktop/Node/'); change the working directory only for that particular REPL session.
Hope it helps!

This has nothing to do with node.js but is rather inherent in the design of Unix (which in turn influences the design of shells on other operating systems).
Processes inherit values from their parent's environment but their environments are distinct.
That terse description of how process environments work has a sometimes unexpected behavior: you cannot change your parent's environment. It was designed this way explicitly for security reasons.
What this means is, when you change the working directory in a process and quits that process your shell's working directory will not be affected. Indeed, your shell's working directory isn't affected even when the process (in this case, node REPL) is running.
This exact question is often asked by people writing shell scripts wanting to write a script that CDs into someplace. But it's also common to find this question asked by people writing other languages such as Perl, Tcl, Ruby etc. (even C).
The answer to this question is always the same regardless of language: it's not possible to CD from another program/script/process.
I'm not sure how Windows handles it so it may be possible to do it there. But it's not possible on Unixen.