feoloap astra

feoloap astra

1619888872

The Introduction to Web Scraping with Node JS

What is web scraping?
Web scraping is extracting data from a website. Why would someone want to scrape the web? Here are four examples:
Scraping social media sites to find trending data
Scraping email addresses from websites that publish public emails
Scraping data from another website to use on your own site
Scraping online stores for sales data, product pictures, etc.
Warnings.
Web scraping is against most website’s terms of service. Your IP address may be banned from a website if you scrape too frequently or maliciously.
What will we need?
For this project we’ll be using Node.js. If you’re not familiar with Node, check out my 3 Best Node.JS Courses.
We’ll also be using two open-sourced npm modules to make today’s task a little easier:
request-promise — Request is a simple HTTP client that allows us to make quick and easy HTTP calls.
cheerio — jQuery for Node.js. Cheerio makes it easy to select, edit, and view DOM elements.
Project Setup.
Create a new project folder. Within that folder create an index.js file. We’ll need to install and require our dependencies. Open up your command line, and install and save: request, request-promise, and cheerio
npm install --save request request-promise cheerio
Then require them in our index.js file:
const rp = require(‘request-promise’);
const cheerio = require(‘cheerio’);
Setting up the Request
request-promise accepts an object as input, and returns a promise. The options object needs to do two things:
Pass in the url we want to scrape.
Tell Cheerio to load the returned HTML so that we can use it.
Here’s what that looks like:
const options = {
uri: https://www.yourURLhere.com,
transform: function (body) {
return cheerio.load(body);
}
};
The uri key is simply the website we want to scrape.
The transform key tells request-promise to take the returned body and load it into Cheerio before returning it to us.
Awesome. We’ve successfully set up our HTTP request options! Here’s what your code should look like so far:
const rp = require(‘request-promise’);
const cheerio = require(‘cheerio’);
const options = {
uri: https://www.yourURLhere.com,
transform: function (body) {
return cheerio.load(body);
}
};
Make the Request
Now that the options are taken care of, we can actually make our request. The boilerplate in the documentation for that looks like this:
rp(OPTIONS)
.then(function (data) {
// REQUEST SUCCEEDED: DO SOMETHING
})
.catch(function (err) {
// REQUEST FAILED: ERROR OF SOME KIND
});
We pass in our options object to request-promise, then wait to see if our request succeeds or fails. Either way, we do something with the returned data.
Knowing what the documentation says to do, lets create our own version:
rp(options)
.then(($) => {
console.log($);
})
.catch((err) => {
console.log(err);
});
The code is pretty similar. The big difference is I’ve used arrow functions. I’ve also logged out the returned data from our HTTP request. We’re going to test to make sure everything is working so far.
Replace the placeholder uri with the website you want to scrape. Then, open up your console and type:
node index.js
// LOGS THE FOLLOWING:
{ [Function: initialize]
fn:
initialize {
constructor: [Circular],
_originalRoot:
{ type: ‘root’,
name: ‘root’,
namespace: ‘http://www.w3.org/1999/xhtml’,
attribs: {},

If you don’t see an error, then everything is working so far — and you just made your first scrape!
Having fun? Want to learn how to build more cool stuff with Node? Check out my 3 Best Node JS Courses
Here is the full code of our boilerplate:

Boilerplate web scraping code
Using the Data
What good is our web scraper if it doesn’t actually return any useful data? This is where the fun begins.
There are numerous things you can do with Cheerio to extract the data that you want. First and foremost, Cheerio’s selector implementation is nearly identical to jQuery’s. So if you know jQuery, this will be a breeze. If not, don’t worry, I’ll show you.
Selectors
The selector method allows you to traverse and select elements in the document. You can get data and set data using a selector. Imagine we have the following HTML in the website we want to scrape:

  • New York
  • Portland
  • Salem
We can select id’s using (#), classes using (.), and elements by their tag names, ex: div. $('.large').text() // New York $('#medium').text() // Portland $('li[class=small]').html() //
  • Salem
  • Looping Just like jQuery, we can also iterate through multiple elements with the each() function. Using the same HTML code as above, we can return the inner text of each li with the following code: $('li').each(function(i, elem) { cities[i] = $(this).text(); }); // New York Portland Salem Finding Imagine we have two lists on our web site:
    • New York
    • Portland
    • Salem
    • Bend
    • Hood River
    • Madras
    We can select each list using their respective ID’s, then find the small city/town within each list: $('#cities').find('.small').text() // Salem $('#towns').find('.small').text() // Madras Finding will search all descendant DOM elements, not just immediate children as shown in this example. Children Children is similar to find. The difference is that children only searches for immediate children of the selected element. $('#cities').children('#c-medium').text(); // Portland Text & HTML Up until this point, all of my examples have included the .text() function. Hopefully you’ve been able to figure out that this function is what gets the text of the selected element. You can also use .html() to return the html of the given element: $('.large').text() // Bend $('.large').html() //
  • Bend
  • Additional Methods There are more methods than I can count, and the documentation for all of them is available here. Chrome Developer Tools Don’t forget, the Chrome Developer Tools are your friend. In Google Chrome, you can easily find element, class, and ID names using: CTRL + SHIFT + C

    Finding class names with chrome dev tools
    As you seen in the above image, I’m able to hover over an element on the page and the element name and class name of the selected element are shown in real-time!
    Limitations
    As Jaye Speaks points out:
    MOST websites modify the DOM using JavaScript. Unfortunately Cheerio doesn’t resolve parsing a modified DOM. Dynamically generated content from procedures leveraging AJAX, client-side logic, and other async procedures are not available to Cheerio.
    Remember this is an introduction to basic scraping. In order to get started you’ll need to find a static website with minimal DOM manipulation.
    Go forth and scrape!
    Thanks for reading. You should have the tools necessary now to go forth and scrape static websites!
    I publish a few articles and tutorials each week, please consider entering your email here if you’d like to be added to my once-weekly email list.
    If tutorials like this interest you and you want to learn more, check out my 3 Best Node JS Courses

    What is GEEK

    Buddha Community

    The Introduction to Web Scraping with Node JS

    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

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    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

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