Shubham Ankit

Shubham Ankit

1565840027

20. Node.js Lessons. Data Streams in Node.JS, fs.ReadStream

Hey all! Our topic for today is Data Streams In Node.js. We will try to learn all the aspects in details for the reason it turns out that on the one hand, common browser JavaScript development lack streams. And on the other hand, knowing and understanding stream principles is necessary for seamless server development because a stream is a versatile way of work with data sources universally used.

We can define two general stream types. The first one is

stream.Readable

It is a built-in class providing streams for reading. Generally, this type itself is never used, while its descendants are quite popular – in particular, we use fs.ReadStream to read from a file. To read from a visitor’s request for its handling, there is a special object familiar to us under its name req, which is the first argument of a request handler.

Stream.Writable

It is a versatile writing method. The very stream.Writable is rarely used, but its descendants – fs.WriteStream and res – are quite common.

There are some other stream types, but the most popular are these two and their variations.

The best way to understand streams is to see how they work in practice. So, right now we’ll start with using fs.ReadStream for reading a file. Let us create a file fs.js:

var fs = require('fs');
 
// fs.ReadStream nherits from stream.Readable
var stream = new fs.ReadStream(__filename);
 
stream.on('readable', function() {
    var data = stream.read();
    console.log(data);
});
 
stream.on('end', function() {
    console.log("THE END");
});

So, we get the module fs connected and create a stream:

var fs = require('fs');
 
var stream = new fs.ReadStream(__filename);

Stream is a JavaScript object receiving information about our resource – in our case, it is a path to the file (__filename) – which can work with this resource. fs.ReadStream implements a standard reading interface described in the stream.Readable class. Let us have a detailed look.

When a stream object new stream.Readable is created, it gets connected to the data source, which is file in our case, and tries to start reading from it. Once it has read something, it imitates the event readable. This event means that all the data have been computed and are contained within an inner stream buffer that can be received using the call read(). Then we can do something with data and wait for the next readable. This cycle will be the same.

Whenever the data source gets empty (however, there are certain sources that never get empty – for example, a random data generator), the file size is limited, so we will have the end, event in the very end meaning there will be no data anymore. Moreover we can call the method destroy() at any step of working with the stream. This method means we do not need the stream anymore and it can be closed, as well as the respective data sources and everything can be cleaned up.

So, let us refer to the original code. Here we create ReadStream, and it immediately wants to open up a file:

var stream = new fs.ReadStream(__filename);

but in our case it doesn’t necessarily mean the same string because any input/output-related operation is performed through libUV. At the same time, libUV has a structure that enables all synchronous input/output handlers to get implemented during the next event loop iteration, or once the current JavaScripthas finished its work. It means, we can seamlessly use all handlers knowing that they will be installed prior to the moment the first data fragment gets read. Launch fs.js.

Look at what has appeared in the console. The first one was the event readable. It outputted data. Right now it is an ordinary buffer, but we can transform it to the string by specifying the coding directly upon the stream opening.

var stream = new fs.ReadStream(__filename, {encoding: 'utf-8'});

Thus, the modification will be automatic. When a file ends, the event endoutputs THE END in the console. Here the file ended almost immediately because it was small at the moment. Let us modify our example a little bit by making a file big.html out of the current file contained in the current directory. Download this HTML file from our repository together with the other lesson materials.

Launch it. The file big.html is big, so the event readable has been initiated several times, and every time we received another data fragment as a buffer. So, let us calculate its length:

var fs = require('fs');
 
// fs.ReadStream nherits from stream.Readable
var stream = new fs.ReadStream("big.html");
 
stream.on('readable', function() {
    var data = stream.read();
    if (data){
        console.log(data.length);
    }
    else {
        console.log('data is null')
    }
});
 
stream.on('end', function() {
    console.log("THE END");
});

Get it launched. These numbers are the read file fragment length. When a stream opens a file, it reads only its part, but not the whole file, and inserts it into its internal variable. The maximum size is exactly 64 KB. Until we call stream.Read, it won’t read further. Once we’ve received the data, the internal buffer cleans up and can be ready for reading another abstract, etc. The last abstract length is 60,959 B. This example has vividly demonstrated the key advantages of stream usage. They help save memory. Whatever is the size our big file, we still handle only its small part at a moment. The second less obvious advantage is versatility of its interface. Here we use the stream ReadStream from the file. But we can replace it any time by any stream from our resource:

var stream = new OurStream("our resource");

It won’t need any change of the left code because streams are, first of all, our interface. So, it means, if theoretically our stream performs all needed events and methods – in particular, it inherits from stream.Readable – everything should be ok. Of course, it will happen only if we do not use any special abilities that only file streams have got. To be more specific, the stream fs.ReadStream has extra events

Here we can see a draft exactly for fs.ReadStream, new events are colored in red. First, it is a file opening, while the last event is its closure. Focus your attention on the fact that if a file is read till its end, the end event occurs followed by close. And if a file is not entirely read – for instance, because of an error or upon calling the destroy method – there will be no end because the file hasn’t been ended. But the event close is always ensured upon a file closure.

Finally, our last, but not least detail here is error handling. So, let us see what will happen, if there is no file.

var stream = new fs.ReadStream("noFile.html");

So, I get it launched. Oops! It crashed! Pay your attention to the fact the streams inherit from EventEmitter. If an error occurs, the whole Node.js process fails. It happens if an error of this kind does not have any handler. That’s why if we do not want our Node.js to fail because of an exception, we should install a handler:

var fs = require('fs');
 
// fs.ReadStream nherits from stream.Readable
var stream = new fs.ReadStream("noFile.html");
 
stream.on('readable', function() {
    var data = stream.read();
    if (data){
        console.log(data.length);
    }
    else {
        console.log('data is null')
    }
});
 
stream.on('error', function(err) {
    if (err.code == 'ENOENT') {
        console.log("File not Found");
    } else {
        console.error(err);
    }
});

So, we use streams to work with data sources in Node.js. Here we’ve analyzed a basic scheme, according to which they work, and a particular example – fs.ReadStream – that can read from a file.

This lesson’s coding can be found in our repository.

#web-development #javascript #node-js

What is GEEK

Buddha Community

20. Node.js Lessons. Data Streams in Node.JS, fs.ReadStream
Marlon  Boyle

Marlon Boyle

1589634120

Hands on with Node.Js Streams | Examples & Approach

Never heard of Node.js? Node.js is an accessible asynchronous environment based on Javascript which contains several core modules helpful for performing various tasks. Node.js is famous worldwide due to its efficiency and being open-source, it brings a lot to the table. Node.js allows the developers to handle multiple requests on a single thread and thereby allowing them more breathing space.

Node.js handles data using two approaches – Buffered and Streamed. In the buffered approach, you have to write the entire data before the receiver may read it. Such an approach doesn’t support its asynchronous paradigm. When it comes to the Streamed approach, the information starts the interpreting process as soon as you enter it.

Before you read further, we would like to inform you that this article is about streams. Streams are an essential part of the Node.js environment. What it stream, and what do they do? What are the different types of streams? We have tried to cover several important questions that may help you in understanding Node.js Streams. Let’s get started.

#nodejs #streams in node.js #using streams in node js #node.js streams #node.js tutorial #data streams

NBB: Ad-hoc CLJS Scripting on Node.js

Nbb

Not babashka. Node.js babashka!?

Ad-hoc CLJS scripting on Node.js.

Status

Experimental. Please report issues here.

Goals and features

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:

  • Fast startup without relying on a custom version of Node.js.
  • Small artifact (current size is around 1.2MB).
  • First class macros.
  • Support building small TUI apps using Reagent.
  • Complement babashka with libraries from the Node.js ecosystem.

Requirements

Nbb requires Node.js v12 or newer.

How does this tool work?

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).

Usage

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

Macros

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.

Startup time

$ 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.

Dependencies

NPM dependencies

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.

Classpath

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.

Current file

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"

Reagent

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]))

Promesa

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.

Js-interop

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:

  • destructuring using :syms
  • property access using .-x notation. In nbb, you must use keywords.

See the example of what is currently supported.

Examples

See the examples directory for small examples.

Also check out these projects built with nbb:

API

See API documentation.

Migrating to shadow-cljs

See this gist on how to convert an nbb script or project to shadow-cljs.

Build

Prequisites:

  • babashka >= 0.4.0
  • Clojure CLI >= 1.10.3.933
  • Node.js 16.5.0 (lower version may work, but this is the one I used to build)

To build:

  • Clone and cd into this repo
  • 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

Hire Dedicated Node.js Developers - Hire Node.js Developers

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.

If you wish to have a strong backend for efficient app performance then have NodeJS at the backend.

WebClues Infotech offers different levels of experienced and expert professionals for your app development needs. So hire a dedicated NodeJS developer from WebClues Infotech with your experience requirement and expertise.

So what are you waiting for? Get your app developed with strong performance parameters from WebClues Infotech

For inquiry click here: https://www.webcluesinfotech.com/hire-nodejs-developer/

Book Free Interview: https://bit.ly/3dDShFg

#hire dedicated node.js developers #hire node.js developers #hire top dedicated node.js developers #hire node.js developers in usa & india #hire node js development company #hire the best node.js developers & programmers

Aria Barnes

Aria Barnes

1622719015

Why use Node.js for Web Development? Benefits and Examples of Apps

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. 

What is Node.js? 

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.

What Are the Advantages of Node.js Web Application Development? 

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. 

Amazing Tech Stack for Web Development 

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: 

  • quick execution and information preparing; 
  • exceptionally reusable code; 
  • the code is not difficult to learn, compose, read, and keep up; 
  • tremendous asset library, a huge number of free aides, and a functioning local area. 

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). 

Designers Can Utilize JavaScript for the Whole Undertaking 

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. 

A Quick Environment for Microservice Development 

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. 

Versatile Web Application Development 

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. 

Control Stream Highlights

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.

 

Final Words

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!

Original Source

#node.js development company in india #node js development company #hire node js developers #hire node.js developers in india #node.js development services #node.js development

Siphiwe  Nair

Siphiwe Nair

1620466520

Your Data Architecture: Simple Best Practices for Your Data Strategy

If you accumulate data on which you base your decision-making as an organization, you should probably think about your data architecture and possible best practices.

If you accumulate data on which you base your decision-making as an organization, you most probably need to think about your data architecture and consider possible best practices. Gaining a competitive edge, remaining customer-centric to the greatest extent possible, and streamlining processes to get on-the-button outcomes can all be traced back to an organization’s capacity to build a future-ready data architecture.

In what follows, we offer a short overview of the overarching capabilities of data architecture. These include user-centricity, elasticity, robustness, and the capacity to ensure the seamless flow of data at all times. Added to these are automation enablement, plus security and data governance considerations. These points from our checklist for what we perceive to be an anticipatory analytics ecosystem.

#big data #data science #big data analytics #data analysis #data architecture #data transformation #data platform #data strategy #cloud data platform #data acquisition