1678410960
Neste tutorial de Javascript, aprenderemos como habilitar e usar módulos ECMAScript no Node.js. Os módulos ECMAScript (em resumo, módulos ES) é um formato de módulos JavaScript que usa importe exportdeclarações:
// An ECMAScript module
// import statement
import myFunc from './my-func';
// export statement
export myOtherFunc(param) {
const result = myFunc(param);
// ....
return otherResult;
}
A partir da versão 13.2.0, Node.js tem suporte estável de módulos ES.
Nesta postagem, você aprenderá como habilitar e usar módulos ES no Node.js.
Antes de continuar, deixe-me recomendar algo para você.
Se você deseja melhorar significativamente seu conhecimento de JavaScript, faça o curso incrivelmente útil "Modern JavaScript From The Beginning 2.0" de Brad Traversy. Use o código do cupom "DMITRI" e ganhe até 20% de desconto!
O formato padrão dos módulos no Node.js é o CommonJS . Para fazer com que o Node.js entenda o formato dos módulos ES, você deve fazê-lo explicitamente.
Node.js usa o formato de módulos ECMAScript se:
Vamos detalhar a primeira ( .mjsextensão) e a segunda ( { "type": "module" }entrada package.json).
Uma maneira fácil de dizer ao Node.js para tratar os módulos no formato ECMAScript é usar a .mjsextensão do arquivo.
O seguinte módulo ES month-from-date.mjs(observe a .mjsextensão do arquivo) exporta uma função monthFromDate(), que determina o nome do mês de uma data arbitrária:
// month-from-date.mjs (ES Module)
const MONTHS = ['January', 'February', 'March','April', 'May', 'June',
'July', 'August', 'September', 'October', 'November', 'December'];
export function monthFromDate(date) {
if (!(date instanceof Date)) {
date = new Date(date);
}
return MONTHS[date.getMonth()];
}
Da mesma forma, outro módulo month.mjsusa a sintaxe do módulo ES importpara importar monthFromDate()a função do 'month-from-date.mjs'módulo. Este módulo também é executado como um script CLI e imprime o nome do mês da string de data passada como um argumento:
// month.mjs (ES Module)
import { monthFromDate } from './month-from-date.mjs';
const dateString = process.argv[2] ?? null;
console.log(monthFromDate(dateString));
Isso é tudo que você precisa para fazer o Node.js usar módulos ES!
Vamos executar month.mjso módulo na linha de comando:
node ./month.mjs "2022-02-01"
Execute o comando na demonstração.
Februaryé impresso no terminal.
Por padrão, .jsos arquivos no Node.js são considerados módulos CommonJS. Para criar .jsarquivos como módulos ES, basta definir "type"o campo como "module"em package.json:
{
"name": "my-app",
"version": "1.0.0",
"type": "module",
// ...
}
Agora, todos .jsos arquivos dentro da pasta que os contêm são package.jsonexecutados como módulos ECMAScript.
Com relação aos módulos do mês, vamos renomear month-from-date.mjsto month-from-date.jse month.mjsto month.js(mantendo a sintaxe importe export), definir "type"o campo como "module"no package.json, e o Node.js executará esses módulos como ECMAScript.
node ./month.js "2022-03-01"
Execute o comando na demonstração.
Marché impresso no terminal.
O especificador é a string literal que representa o caminho de onde importar o módulo.
No exemplo abaixo 'path'está um especificador:
// 'path' is the specifier
import module from 'path';
Existem 3 tipos de especificadores no Node.js: relativo, simples e absoluto.
A importação de um módulo usando um especificador relativo resolveria o caminho do módulo importado em relação ao local atual (de importação) do módulo.
Os especificadores relativos geralmente começam com '.', '..'ou './':
// Relative specifiers:
import module1 from './module1.js';
import module2 from '../folder/module2.mjs';
Ao usar especificadores relativos, a indicação da extensão do arquivo ( .js, '.mjs', etc.) é obrigatória.
Um especificador simples começa com um nome de módulo (não começa com '.', './', '..', '/') e importa módulos de node_modulesou os módulos integrados do Node.js.
Por exemplo, se você instalou o lodash-espacote em node_modules, poderá acessar esse módulo usando um especificador simples:
// Bare specifiers:
import lodash from 'lodash-es';
import intersection from 'lodash-es/intersection';
Usando especificadores simples, você também pode importar os módulos integrados do Node.js:
import fs from 'fs';
Um especificador absoluto importa módulos usando um caminho absoluto:
// Absolute specifier:
import module from 'file:///usr/opt/module.js';
Observe a presença do file://prefixo nos especificadores absolutos.
O mecanismo de importação padrão dos módulos ES sempre avalia e importa o módulo especificado no import module from 'path'— independentemente de você usar o módulo ou não.
Mas às vezes você pode querer importar os módulos dinamicamente, caso em que você pode invocar a função assíncrona import('./path-to-module'):
async function loadModule() {
const {
default: defaultComponent,
component1
} = await import('./path-to-module');
// ...
}
loadModule();
import('./path-to-module')carrega o módulo de forma assíncrona e retorna uma promessa que resolve os componentes do módulo importado: defaultpropriedade como a importação padrão e as importações nomeadas como propriedades com os mesmos nomes.
Por exemplo, vamos melhorar month.jso script para carregar month-from-date.jso módulo somente quando o usuário definir o argumento de data:
// month.js (ES Module)
const dateString = process.argv[2] ?? null;
if (dateString === null) {
console.log('Please indicate date argument');
} else {
(async function() {
const { monthFromDate } = await import('./month-from-date.js');
console.log(monthFromDate(dateString));
})();
}
const { monthFromDate } = await import('./month-from-date.mjs')carrega o módulo dinamicamente e atribui a exportação nomeada monthFromDatea uma variável com o mesmo nome.
node ./month.js "2022-04-01"
Execute o comando na demonstração.
Aprilestá logado no terminal.
Você pode estar em uma situação em que precisa importar um módulo CommonJS de um módulo ES e vice-versa.
Felizmente, o Node.js permite que um módulo ES inclua um módulo CommonJS como uma importação padrão:
// ES module
import defaultComponent from './module.commonjs.js';
// use `defaultComponent`...
Quando importado em um módulo ES, o module.exportsdo módulo CommonJS torna-se a importação padrão. As importações nomeadas de um módulo CommonJS, no entanto, não são suportadas.
No entanto, a require()função do formato CommonJS não pode importar um módulo ES. Em vez disso, você pode usar a função async import()dentro do CommonJS para carregar um módulo ES:
// CommonJS module
async function loadESModule() {
const {
default: defaultComponent,
component1
} = await import('./module.es.mjs');
// ...
}
loadESModule();
Eu recomendo o máximo possível para evitar a mistura de formatos de módulos.
Dentro do escopo do módulo ECMAScript não estão disponíveis as variáveis específicas do CommonJS como:
No entanto, você pode usar import.meta.urlpara determinar o caminho absoluto do módulo atual:
// An ES module at path "/usr/opt/module.mjs"
console.log(import.meta.url); // "file:///usr/opt/module.mjs"
Node.js oferece suporte a módulos ES quando a extensão do módulo é .mjs, ou a pasta mais próxima do módulo package.jsoncontém { “type”: “module” }.
Então você pode importar módulos usando:
Você pode importar dinamicamente um módulo usando import('./path-to-module')a sintaxe.
Embora não seja desejável, mas às vezes necessário, você pode importar um módulo CommonJS de um módulo ES usando a import defaultImport from './common.js'instrução. O module.exportsdo CommonJS torna-se a importação padrão defaultImportdentro do módulo ES.
Fonte do artigo original em: https://dmitripavlutin.com
1632537859
Not babashka. Node.js babashka!?
Ad-hoc CLJS scripting on Node.js.
Experimental. Please report issues here.
Nbb's main goal is to make it easy to get started with ad hoc CLJS scripting on Node.js.
Additional goals and features are:
Nbb requires Node.js v12 or newer.
CLJS code is evaluated through SCI, the same interpreter that powers babashka. Because SCI works with advanced compilation, the bundle size, especially when combined with other dependencies, is smaller than what you get with self-hosted CLJS. That makes startup faster. The trade-off is that execution is less performant and that only a subset of CLJS is available (e.g. no deftype, yet).
Install nbb
from NPM:
$ npm install nbb -g
Omit -g
for a local install.
Try out an expression:
$ nbb -e '(+ 1 2 3)'
6
And then install some other NPM libraries to use in the script. E.g.:
$ npm install csv-parse shelljs zx
Create a script which uses the NPM libraries:
(ns script
(:require ["csv-parse/lib/sync$default" :as csv-parse]
["fs" :as fs]
["path" :as path]
["shelljs$default" :as sh]
["term-size$default" :as term-size]
["zx$default" :as zx]
["zx$fs" :as zxfs]
[nbb.core :refer [*file*]]))
(prn (path/resolve "."))
(prn (term-size))
(println (count (str (fs/readFileSync *file*))))
(prn (sh/ls "."))
(prn (csv-parse "foo,bar"))
(prn (zxfs/existsSync *file*))
(zx/$ #js ["ls"])
Call the script:
$ nbb script.cljs
"/private/tmp/test-script"
#js {:columns 216, :rows 47}
510
#js ["node_modules" "package-lock.json" "package.json" "script.cljs"]
#js [#js ["foo" "bar"]]
true
$ ls
node_modules
package-lock.json
package.json
script.cljs
Nbb has first class support for macros: you can define them right inside your .cljs
file, like you are used to from JVM Clojure. Consider the plet
macro to make working with promises more palatable:
(defmacro plet
[bindings & body]
(let [binding-pairs (reverse (partition 2 bindings))
body (cons 'do body)]
(reduce (fn [body [sym expr]]
(let [expr (list '.resolve 'js/Promise expr)]
(list '.then expr (list 'clojure.core/fn (vector sym)
body))))
body
binding-pairs)))
Using this macro we can look async code more like sync code. Consider this puppeteer example:
(-> (.launch puppeteer)
(.then (fn [browser]
(-> (.newPage browser)
(.then (fn [page]
(-> (.goto page "https://clojure.org")
(.then #(.screenshot page #js{:path "screenshot.png"}))
(.catch #(js/console.log %))
(.then #(.close browser)))))))))
Using plet
this becomes:
(plet [browser (.launch puppeteer)
page (.newPage browser)
_ (.goto page "https://clojure.org")
_ (-> (.screenshot page #js{:path "screenshot.png"})
(.catch #(js/console.log %)))]
(.close browser))
See the puppeteer example for the full code.
Since v0.0.36, nbb includes promesa which is a library to deal with promises. The above plet
macro is similar to promesa.core/let
.
$ time nbb -e '(+ 1 2 3)'
6
nbb -e '(+ 1 2 3)' 0.17s user 0.02s system 109% cpu 0.168 total
The baseline startup time for a script is about 170ms seconds on my laptop. When invoked via npx
this adds another 300ms or so, so for faster startup, either use a globally installed nbb
or use $(npm bin)/nbb script.cljs
to bypass npx
.
Nbb does not depend on any NPM dependencies. All NPM libraries loaded by a script are resolved relative to that script. When using the Reagent module, React is resolved in the same way as any other NPM library.
To load .cljs
files from local paths or dependencies, you can use the --classpath
argument. The current dir is added to the classpath automatically. So if there is a file foo/bar.cljs
relative to your current dir, then you can load it via (:require [foo.bar :as fb])
. Note that nbb
uses the same naming conventions for namespaces and directories as other Clojure tools: foo-bar
in the namespace name becomes foo_bar
in the directory name.
To load dependencies from the Clojure ecosystem, you can use the Clojure CLI or babashka to download them and produce a classpath:
$ classpath="$(clojure -A:nbb -Spath -Sdeps '{:aliases {:nbb {:replace-deps {com.github.seancorfield/honeysql {:git/tag "v2.0.0-rc5" :git/sha "01c3a55"}}}}}')"
and then feed it to the --classpath
argument:
$ nbb --classpath "$classpath" -e "(require '[honey.sql :as sql]) (sql/format {:select :foo :from :bar :where [:= :baz 2]})"
["SELECT foo FROM bar WHERE baz = ?" 2]
Currently nbb
only reads from directories, not jar files, so you are encouraged to use git libs. Support for .jar
files will be added later.
The name of the file that is currently being executed is available via nbb.core/*file*
or on the metadata of vars:
(ns foo
(:require [nbb.core :refer [*file*]]))
(prn *file*) ;; "/private/tmp/foo.cljs"
(defn f [])
(prn (:file (meta #'f))) ;; "/private/tmp/foo.cljs"
Nbb includes reagent.core
which will be lazily loaded when required. You can use this together with ink to create a TUI application:
$ npm install ink
ink-demo.cljs
:
(ns ink-demo
(:require ["ink" :refer [render Text]]
[reagent.core :as r]))
(defonce state (r/atom 0))
(doseq [n (range 1 11)]
(js/setTimeout #(swap! state inc) (* n 500)))
(defn hello []
[:> Text {:color "green"} "Hello, world! " @state])
(render (r/as-element [hello]))
Working with callbacks and promises can become tedious. Since nbb v0.0.36 the promesa.core
namespace is included with the let
and do!
macros. An example:
(ns prom
(:require [promesa.core :as p]))
(defn sleep [ms]
(js/Promise.
(fn [resolve _]
(js/setTimeout resolve ms))))
(defn do-stuff
[]
(p/do!
(println "Doing stuff which takes a while")
(sleep 1000)
1))
(p/let [a (do-stuff)
b (inc a)
c (do-stuff)
d (+ b c)]
(prn d))
$ nbb prom.cljs
Doing stuff which takes a while
Doing stuff which takes a while
3
Also see API docs.
Since nbb v0.0.75 applied-science/js-interop is available:
(ns example
(:require [applied-science.js-interop :as j]))
(def o (j/lit {:a 1 :b 2 :c {:d 1}}))
(prn (j/select-keys o [:a :b])) ;; #js {:a 1, :b 2}
(prn (j/get-in o [:c :d])) ;; 1
Most of this library is supported in nbb, except the following:
:syms
.-x
notation. In nbb, you must use keywords.See the example of what is currently supported.
See the examples directory for small examples.
Also check out these projects built with nbb:
See API documentation.
See this gist on how to convert an nbb script or project to shadow-cljs.
Prequisites:
To build:
bb release
Run bb tasks
for more project-related tasks.
Download Details:
Author: borkdude
Download Link: Download The Source Code
Official Website: https://github.com/borkdude/nbb
License: EPL-1.0
#node #javascript
1616671994
If you look at the backend technology used by today’s most popular apps there is one thing you would find common among them and that is the use of NodeJS Framework. Yes, the NodeJS framework is that effective and successful.
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1622719015
Front-end web development has been overwhelmed by JavaScript highlights for quite a long time. Google, Facebook, Wikipedia, and most of all online pages use JS for customer side activities. As of late, it additionally made a shift to cross-platform mobile development as a main technology in React Native, Nativescript, Apache Cordova, and other crossover devices.
Throughout the most recent couple of years, Node.js moved to backend development as well. Designers need to utilize a similar tech stack for the whole web project without learning another language for server-side development. Node.js is a device that adjusts JS usefulness and syntax to the backend.
Node.js isn’t a language, or library, or system. It’s a runtime situation: commonly JavaScript needs a program to work, however Node.js makes appropriate settings for JS to run outside of the program. It’s based on a JavaScript V8 motor that can run in Chrome, different programs, or independently.
The extent of V8 is to change JS program situated code into machine code — so JS turns into a broadly useful language and can be perceived by servers. This is one of the advantages of utilizing Node.js in web application development: it expands the usefulness of JavaScript, permitting designers to coordinate the language with APIs, different languages, and outside libraries.
Of late, organizations have been effectively changing from their backend tech stacks to Node.js. LinkedIn picked Node.js over Ruby on Rails since it took care of expanding responsibility better and decreased the quantity of servers by multiple times. PayPal and Netflix did something comparative, just they had a goal to change their design to microservices. We should investigate the motivations to pick Node.JS for web application development and when we are planning to hire node js developers.
The principal thing that makes Node.js a go-to environment for web development is its JavaScript legacy. It’s the most well known language right now with a great many free devices and a functioning local area. Node.js, because of its association with JS, immediately rose in ubiquity — presently it has in excess of 368 million downloads and a great many free tools in the bundle module.
Alongside prevalence, Node.js additionally acquired the fundamental JS benefits:
In addition, it’s a piece of a well known MEAN tech stack (the blend of MongoDB, Express.js, Angular, and Node.js — four tools that handle all vital parts of web application development).
This is perhaps the most clear advantage of Node.js web application development. JavaScript is an unquestionable requirement for web development. Regardless of whether you construct a multi-page or single-page application, you need to know JS well. On the off chance that you are now OK with JavaScript, learning Node.js won’t be an issue. Grammar, fundamental usefulness, primary standards — every one of these things are comparable.
In the event that you have JS designers in your group, it will be simpler for them to learn JS-based Node than a totally new dialect. What’s more, the front-end and back-end codebase will be basically the same, simple to peruse, and keep up — in light of the fact that they are both JS-based.
There’s another motivation behind why Node.js got famous so rapidly. The environment suits well the idea of microservice development (spilling stone monument usefulness into handfuls or many more modest administrations).
Microservices need to speak with one another rapidly — and Node.js is probably the quickest device in information handling. Among the fundamental Node.js benefits for programming development are its non-obstructing algorithms.
Node.js measures a few demands all at once without trusting that the first will be concluded. Many microservices can send messages to one another, and they will be gotten and addressed all the while.
Node.js was worked in view of adaptability — its name really says it. The environment permits numerous hubs to run all the while and speak with one another. Here’s the reason Node.js adaptability is better than other web backend development arrangements.
Node.js has a module that is liable for load adjusting for each running CPU center. This is one of numerous Node.js module benefits: you can run various hubs all at once, and the environment will naturally adjust the responsibility.
Node.js permits even apportioning: you can part your application into various situations. You show various forms of the application to different clients, in light of their age, interests, area, language, and so on. This builds personalization and diminishes responsibility. Hub accomplishes this with kid measures — tasks that rapidly speak with one another and share a similar root.
What’s more, Node’s non-hindering solicitation handling framework adds to fast, letting applications measure a great many solicitations.
Numerous designers consider nonconcurrent to be one of the two impediments and benefits of Node.js web application development. In Node, at whatever point the capacity is executed, the code consequently sends a callback. As the quantity of capacities develops, so does the number of callbacks — and you end up in a circumstance known as the callback damnation.
In any case, Node.js offers an exit plan. You can utilize systems that will plan capacities and sort through callbacks. Systems will associate comparable capacities consequently — so you can track down an essential component via search or in an envelope. At that point, there’s no compelling reason to look through callbacks.
So, these are some of the top benefits of Nodejs in web application development. This is how Nodejs is contributing a lot to the field of web application development.
I hope now you are totally aware of the whole process of how Nodejs is really important for your web project. If you are looking to hire a node js development company in India then I would suggest that you take a little consultancy too whenever you call.
Good Luck!
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1616839211
Top organizations and start-ups hire Node.js developers from SISGAIN for their strategic software development projects in Illinois, USA. On the off chance that you are searching for a first rate innovation to assemble a constant Node.js web application development or a module, Node.js applications are the most appropriate alternative to pick. As Leading Node.js development company, we leverage our profound information on its segments and convey solutions that bring noteworthy business results. For more information email us at hello@sisgain.com
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1625114985
Node.js is a prominent tech trend in the space of web and mobile application development. It has been proven very efficient and useful for a variety of application development. Thus, all business owners are eager to leverage this technology for creating their applications.
Are you striving to develop an application using Node.js? But can’t decide which company to hire for NodeJS app development? Well! Don’t stress over it, as the following list of NodeJS app development companies is going to help you find the best partner.
Let’s take a glance at top NodeJS application development companies to hire developers in 2021 for developing a mind-blowing application solution.
Before enlisting companies, I would like to say that every company has a foundation on which they thrive. Their end goals, qualities, and excellence define their competence. Thus, I prepared this list by considering a number of aspects. While making this list, I have considered the following aspects:
I believe this list will help you out in choosing the best NodeJS service provider company. So, now let’s explore the top NodeJS developer companies to choose from in 2021.
#1. JSGuru
JSGuru is a top-rated NodeJS app development company with an innovative team of dedicated NodeJS developers engaged in catering best-class UI/UX design, software products, and AWS professional services.
It is a team of one of the most talented developers to hire for all types of innovative solution development, including social media, dating, enterprise, and business-oriented solutions. The company has worked for years with a number of startups and launched a variety of products by collaborating with big-name corporations like T-systems.
If you want to hire NodeJS developers to secure an outstanding application, I would definitely suggest them. They serve in the area of eLearning, FinTech, eCommerce, Telecommunications, Mobile Device Management, and more.
Ratings: 4.9/5.0
Founded: 2006
Headquarters: Banja Luka, Bosnia, and Herzegovina
Price: Starting from $50/hour
Visit Website - https://www.valuecoders.com/blog/technology-and-apps/top-node-js-app-development-companies
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