Kako modularno programiranje djeluje u Node.js

Moduli su jedno od temeljnih obilježja Node.js.

Kada izrađujete aplikaciju, jer kod postaje sve složeniji, ne možete staviti cijeli svoj kôd u jednu datoteku.

Kako ovo postaje neupravljivo, Nodeov obrazac modula možete koristiti za pisanje različitih datoteka i izvoz (uključujući funkcije, objekte i metode) u glavnu datoteku.

Sad se možete pitati - što je zapravo a module?

Jednostavno rečeno, a modulenije ništa drugo nego JavaScript datoteka. To je to.

Pomoću modularne funkcionalnosti Node-a možemo uvesti vlastite vanjske datoteke, osnovne (matične) čvorne module i NPM-module. U ovom ćemo članku detaljno razmotriti svaku od njih.

Kako uvesti vlastite datoteke

U ovom ćemo članku razgovarati o tome kako možemo izvesti i uvesti vlastite datoteke.

U osnovi postoje dvije datoteke calculate.js:, odakle ćemo izvoziti i main.jsdo mjesta na koju ćemo uvesti tu datoteku.

mduleexport.png

Obje datoteke imamo u istoj mapi kako bi bilo jednostavnije.

image.png

Kako uvesti funkciju

//---- Exported file [calculate.js] ---- const add = (a,b)=>{ return a + b } module.exports = add 

Ovdje izvozimo funkciju koja se naziva addupotreba module.exports. Tada se ova funkcija uvozi u drugu datoteku pomoću requiremetode.

U Nodeu se svaka datoteka naziva a modulei exportssvojstvo je modula Object.

Sada možemo pozvati funkciju u drugoj datoteci, odnosno main.jsprosljeđivanjem argumenata kao što je prikazano u nastavku.

//------ Main File[main.js] ---- const add = require('./calculate') //name of the desired file const result = add(2,4) console.log(result); //Output : 6 

Kako uvesti objekt

Također možemo izvesti cijeli objekt i pristupiti različitim metodama u njemu.

//---- Exported file [calculate.js] ---- const add = { result : (a,b)=>{ return a + b } } module.exports = add 

Izvezli smo objekt addi uveli ga u našu glavnu datoteku pomoću requiremetode.

Sada možemo pristupiti resultmetodi addobjekta pomoću .operatora točke:

//---- Main file[main.js] ---- const add = require('./calculate') const result = add.result(5,8) console.log(result) //Output : 13 

Drugi način na koji možemo izvesti gornji objekt je izvoz samo one metode koja nam je potrebna, a ne cijelog objekta.

//---- Exported file [calculate.js] ---- const add = { result : (a,b)=>{ return a + b } } module.exports = add.result 

Kao što vidite, resultmetodu uvozimo u addobjekt. Dakle, ova se metoda može izravno pozvati u glavnoj datoteci.

Ovo je dobra praksa ako vam ne treba cijeli objekt, već su mu potrebne samo neke metode / funkcije. To također čini naš kod sigurnijim.

//---- Main file[main.js] ---- const add = require('./calculate') const result = add(5,8) console.log(result) //Output : 13 

Kako uvesti konstruktor funkcija:

Konstruktor funkcije u osnovi se koristi za stvaranje nove instance objekta koji posjeduje ista svojstva kao i glavni objekt / funkcija.

U donjem slučaju kreiramo novu instancu objekta 'Dodaj' pomoću newključne riječi. Taj se postupak u kojem kreiramo instancu objekta naziva 'instancijacija'.

Zatim izvozimo ovu instancu koristeći module.exports:

//---- Exported file [calculate.js] ---- function Add (){ this.result = (a,b)=>{ return a + b } } module.exports = new Add() 

Sada ga možemo uvesti u našu glavnu datoteku i pristupiti metodi 'rezultat' unutar nje, kako bismo dobili izračunatu vrijednost.

//---- Main file[main.js] ---- const add = require('./calculate2') const result = add.result(1,3) console.log(result); //Output : 4 

Na ovaj način možemo izvesti i uvesti konstruktor funkcije.

Postoji još jedan način na koji to možemo učiniti, a to je stvaranjem nove instance u glavnoj datoteci, a ne u izvoženoj datoteci kao što je gore prikazano module.exports = new Add().

Vidjet ćemo kako će to funkcionirati kada izvežemo ES6 klase koje rade slično konstruktorima funkcija.

Kako uvesti ES6 klase

classje posebna vrsta funkcije u kojoj classključna riječ pomaže u inicijalizaciji. constructorMetodu koristi za spremanje svojstava.

Sada ćemo izvesti cijeli classkoristeći module.exports:

//---- Exported file [calculate.js] ---- const Add = class{ constructor(a,b){ this.a = a; this.b = b; } result(){ return this.a + this.b } } module.exports = Add; 

Sada u našoj glavnoj datoteci kreiramo novu instancu pomoću newključne riječi i pristupamo resultmetodi kako bismo dobili izračunatu vrijednost.

 //---- Main file[main.js] ---- const add = require('./calculate') const result = new add(2,5) console.log(result.result()); //Output : 7 

Kako uvesti osnovne (matične) module čvora

Umjesto da svaki put izrađujemo vlastite prilagođene module, Node nudi skup modula koji nam olakšavaju život.

Razgovarat ćemo o nekim modulima, ali cijeli popis možete pronaći u službenom dokumentu API-ja čvora ovdje.

Uvoz modula čvora sličan je načinu na koji uvozite vlastite module. Istu require()funkciju upotrebljavate za pristup u vlastitoj datoteci.

But there are some modules which you may have used unknowingly which do not need to be imported. For example console.log() – we have used the console module many times without fetching it in our own local file as these methods are available globally.

Let's look at one of the Core Native Modules which is File System (fs).

There are n number of operations we can perform with the file system module such as reading a file, writing a file, and updating it, to name a few.

We are going to use the fs module to read a file. Even in this method, there are two ways we can perform this action: one by using the synchronous function fs.readFileSync(), and the other by asynchronous function fs.readFile().

We'll discuss synchronous-asynchronous Node functions in future posts.

Today, we'll use the asynchronous version, that is fs.readFile().

For this example, we have created two files: main.js, where we are going to perform the file reading operation, and file.txt which is the file we are going to read.

image.png

Thefile.txt contains some text in it.

Hello World!

Now, we use the fs module to read the file, without importing it, as shown below:

fs.readFile('./file.txt','utf-8',(err,data)=>{ if (err) throw err console.log(data); })

It will throw an error as fs is not defined. That is because the file system fs module is not available globally like the console module is.

ReferenceError: fs is not defined at Object. (C:\Users\Sarvesh Kadam\Desktop\Training\blog\code snippets\Node Modular Pattern\main.js:3:1) at Module._compile (internal/modules/cjs/loader.js:1256:30) at Object.Module._extensions..js (internal/modules/cjs/loader.js:1277:10) at Module.load (internal/modules/cjs/loader.js:1105:32) at Function.Module._load (internal/modules/cjs/loader.js:967:14) at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:60:12) at internal/main/run_main_module.js:17:47 

Therefore, we need to import all the data from the file system module using the require() function and store all that data in a variable fs.

const fs = require('fs') fs.readFile('./file.txt','utf-8',(err,data)=>{ if (err) throw err console.log(data); })

Now you can name that variable anything. I named it fs for readability and it's the standard which most developers follow.

Using the fs variable we can access the readFile() method where we passed three arguments Those arguments are file path, character encoding utf-8, and the callback function to give an output.

You might ask why we're passing utf-8 as our argument in the readFile()?

Because it encodes the value and gives the text as an output rather than giving a buffer as shown below:

The callback function, in turn, has two arguments: an error (err) and the actual content in the file (data). Then we print that data in the console.

//Output: Hello World! 

How to Import NPM Modules

So what exactly is Node Package Manager?

Paket je dio koda kojim upravlja Upravitelj paketa. Instaliranje i ažuriranje paketa upravlja softverom.

NPM prema službenoj dokumentaciji:

NPM je najveći svjetski registar softvera. Programeri otvorenog koda sa svih kontinenata koriste npm za dijeljenje i posuđivanje paketa, a mnoge organizacije koriste npm i za upravljanje privatnim razvojem.

Dakle, u NPM-u koristimo tuđi kod otvorenog koda kojim upravlja NPM tako što ga uvozimo u naš projekt.

NPM obično dolazi s Node JS kada ga preuzmete. Možete provjeriti je li NPM instaliran na vašem računalu jednostavnim pokretanjem naredbe npm -vna naredbenom retku. Ako vrati neki broj verzije, to znači da je NPM uspješno instaliran.

NPM ima svoj registar na npmjs.com gdje možete otkriti pakete koje možete koristiti.

Let's look at one of the packages called chalk which is basically used for terminal styling.

chalknpm2.jpg

In the above figure, we can see the weekly downloads of the package which suggests how popular is it.

Also, you can see that this package has dependencies in it. So this module which will serve as a dependency on our project is itself dependent on other modules.

This entire management process is taken care of by the Package Manager.

Even the source code is which is present on GitHub is given to us. We can navigate to it and verify if there are any open issues present.

One more thing before moving forward: the NPM packages come in different versions. The pattern which the version follows is semantic versioning.

As you can see, the latest version of the chalk module when I wrote this article is 4.1.0.

It follows the semantic versioning Major_changes.Minor_changes.Patch pattern.

Major_changes, as the name stands, are the significant changes made on the module which might affect your existing code.

Minor_changes are new enhancements or features along with defect fixes that have been added which should not affect your existing code.

Patch is the small bug fixes that will not crash your existing code.

You can learn more about semantic versioning on semver.org.

How to Install NPM

Now to import any package from NPM, you first need to initialize NPM on your local project folder by running the command on the command prompt:

npm init 

Once you run the above command, it will ask you for some data as shown below such as package name, version, and so on.

Much of this data can be kept as default as mentioned in the Round brackets ().

Also, the fields such as author and license are for the folks who created those NPM packages.

On the other hand, we are just importing and using them to create our own application.

package name: (code_npm) code_npm version: (1.0.0) 1.0.0 description: npm demo entry point: (index.js) index.js test command: test git repository: keywords: npm test author: Sarvesh license: (ISC) 

Once you enter all the fields, it will create a JSON file with values that have the above properties, and it'll ask you for confirmation like this:

Is this OK? (yes) yes 

Once you've confirmed yes it will create a package.json file with all the data you entered as illustrated below:

{ "name": "code_npm", "version": "1.0.0", "description": "npm demo", "main": "index.js", "scripts": { "test": "echo \"Error: no test specified\" && exit 1" }, "keywords": [ "npm", "test" ], "author": "Sarvesh", "license": "ISC" } 

Also, you can see a script object that has a test property added. You can run it using the npm test command and it will give back the desired output like this:

"Error: no test specified" 

Now instead of doing this elongated method of initializing NPM and entering the custom properties values, you can simply run the command:

npm init -y 

Once you run this command, it will directly create a package.json file with the default values.

pkgjson.PNG

Now to install the latest version of the chalk package in your project, you need to execute the command:

npm install chalk 

You can also install any specific version you need of chalk by just adding @version number as shown below. Also instead of install you can simply put the short-hand i flag which stands for installation:

npm i [email protected] 

This will install two things, a node_modules folder, and a package-lock.json file.

folderdir.PNG

Also, it will add a new property called dependencies to our package.json file which contains the name of the package installed and its version.

"dependencies": { "chalk": "^4.0.0" } 

The node_module folder contains the packages folder and its dependency's folders. It gets modifies as and when the npm package gets installed.

The package-lock.json contains the code which makes NPM faster and more secure.

"chalk": { "version": "4.0.0", "resolved": "//registry.npmjs.org/chalk/-/chalk-4.0.0.tgz", "integrity": "sha512-N9oWFcegS0sFr9oh1oz2d7Npos6vNoWW9HvtCg5N1KRFpUhaAhvTv5Y58g880fZaEYSNm3qDz8SU1UrGvp+n7A==", "requires": { "ansi-styles": "^4.1.0", "supports-color": "^7.1.0" } 

It mainly contains properties such as version, which is the semantic version number.

The resolved property is the directory or location from which the package was fetched. In this case it was fetched from chalk.

The integrity property is to make sure that we get the same code if we install the dependency again.

The requires object property represents the dependency of the chalk package.

Note: Do not make any changes to these two files node_modules and package-lock.json

How to Use NPM

Now once we've installed chalk to our project, we can import it to our root project file using the require() method. Then we can store that module in a variable called chalk.

const chalk = require('chalk') console.log(chalk.red("Hello World"))

Using the red() method of the chalk package, we have styled the "Hello World" text color in red.

On running the command node index.js we get the following output:

chalkop.png

Now there are many ways you can style your command line output using the chalk package. For more information you can refer to the Chalk official document on NPM.

Also, you can install the NPM packages globally (that is, on our operating system) rather than installing it in your local project by adding the -g flag on the command line (which stands for global, as mentioned below):

npm i nodemon -g 

This global package will not affect our package.json in any way since it is not installed locally.

We have installed the nodemon package globally which is used for automatic restart of a Node application when file changes in the directory are observed.

You can refer to nodemon for more information.

We can use the nodemon package by running the application using this command:

nodemon index.js 

It works similarly to node index.js, except it keeps an eye on the file changes and it restarts the application once changes are detected.

[nodemon] 2.0.6 [nodemon] to restart at any time, enter `rs` [nodemon] watching path(s): *.* [nodemon] watching extensions: js,mjs,json [nodemon] starting `node index.js` Hello World 

Note: The chalk styling will probably not work when you used nodemon.

Finally, we will go through the dev dependencies. There are some NPM packages or modules which we won't need in our project's production environment, but only for our development requirements.

We can install these modules in our project using the dev flag as shown below:

 npm i nodemon --save-dev 

It then creates a new property in the package.json called devDependencies:

"devDependencies": { "nodemon": "^2.0.6" } 

Conclusion

Using Node's Module Pattern, we can import from our own files by exporting them in form of functions, objects, function constructors, and ES6 classes.

And Node has its own set of Core (Native) Modules which we can use. Some of them are available globally, while some of them need to be imported locally in your project/folder.

NPM is a package manager that manages 3rd party open source code which we can use in our project. Before using NPM modules, you need to initialize NPM locally using npm init on your command line in the root of your project folder.

Pomoću naredbe možete instalirati bilo koji NPM paket npm i . A NPM paket možete instalirati globalno koristeći -gzastavicu. Također se paket može učiniti razvojno ovisnim pomoću --save-devzastavice.

Hvala na čitanju! Ako vam se sviđa ovaj članak, obratite mi se na Twitteru dok nastavljam dokumentirati svoje učenje.