Why and when to use Node.js? [duplicate]

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7 Answers

90%

Cloning a node copies all of its attributes and their values, including intrinsic (inline) listeners. It does not copy event listeners added using addEventListener() or those assigned to element properties (e.g., node.onclick = someFunction). Additionally, for a <canvas> element, the painted image is not copied. , If true, then node and its whole subtree—including text that may be in child Text nodes—is also copied. , If the original node has an id attribute, and the clone will be placed in the same document, then you should modify the clone's ID to be unique. , Also, name attributes may need to be modified also, depending on whether duplicate names are expected.

let newClone = node.cloneNode([deep])
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88%

Sometimes you need to remove duplicate values from an array in JavaScript. Actually, it’s straightforward in modern JavaScript to quickly create an array of unique values using the Set data structure.,This is a welcoming use-case for the Set data structure. JavaScript introduced the Set data structure as part of ES2015 describing itself as a collection of unique values.,You can also use JavaScript’s Array.from() method which creates an array from an iterable. The Set data structure is an iterable object and a valid parameter for this approach:, Get the Part Before a Character in a String in JavaScript or Node.js

Here‘s an example extracting the unique values from an array of items:

const items = [1, 2, 3, 2, 3, 1, 5]

const unique = [...new Set(items)]
// [1, 2, 3, 5]
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72%

const names = ['John', 'Paul', 'George', 'Ringo', 'John'];

let unique = [...new Set(names)];
console.log(unique); // 'John', 'Paul', 'George', 'Ringo'
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65%

I am using Nodejs Azure function,Apim gateway and cosmosdb combination with vs code as ide.,When i try to use application insight sdk instrumentation- log, request and dependencies have duplicates in app insight portal.,We host our solution and application including application insight at west us,Linux: tmp/appInsights-node/instrumentationKey

//app insights config.
let appInsights = require("applicationinsights");
appInsights.setup("<instrumentation_key>")
    .setAutoDependencyCorrelation(true)
    .setAutoCollectRequests(true)
    .setAutoCollectPerformance(true, true)
    .setAutoCollectExceptions(true)
    .setAutoCollectDependencies(true)
    .setAutoCollectConsole(true)
    .setUseDiskRetryCaching(true)
    .setSendLiveMetrics(false)
    .setDistributedTracingMode(appInsights.DistributedTracingModes.AI_AND_W3C)
    .start();

//host.json
{
  "logging": {
    "fileLoggingMode": "always",
    "logLevel": {
      "default": "Information",
      "Host.Results": "Error",
      "Function": "Error",
      "Host.Aggregator": "Trace"
    }
  }
}

Note: **codeless instrumentation key is not provided only host.json config is given.**
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75%

FS constants File access constants File copy constants File open constants File type constants File mode constants ,fs.constants FS constants File access constants File copy constants File open constants File type constants File mode constants ,Node-API version matrix,Crypto constants OpenSSL options OpenSSL engine constants Other OpenSSL constants Node.js crypto constants

Linux and Mac:

$ mkdir~/projects
$ cd~/projects

Windows CMD:

> mkdir % USERPROFILE % \projects >
   cd % USERPROFILE % \projects

Windows PowerShell:

> mkdir $env: USERPROFILE\ projects >
   cd $env: USERPROFILE\ projects

Open hello-world.js in any preferred text editor and paste in the following content:

const http = require('http');

const hostname = '127.0.0.1';
const port = 3000;

const server = http.createServer((req, res) => {
   res.statusCode = 200;
   res.setHeader('Content-Type', 'text/plain');
   res.end('Hello, World!\n');
});

server.listen(port, hostname, () => {
   console.log(`Server running at http://${hostname}:${port}/`);
});

Save the file, go back to the terminal window, and enter the following command:

$ node hello - world.js

Output like this should appear in the terminal:

Server running at http: //127.0.0.1:3000/
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40%

However, what if we want to export this function directly, and not as the property of some object? We can overwrite exports to do this, but we must not treat it as a global variable then:,When this is done, anyone requiring “a.js” will be given an object with the property function “verifyPassword”:,To enable debug lines, simply run this code with the environment variable DEBUG set to “app” or “*”:,In many asynchronous functions, the return value has almost no significance, so this approach often makes it easy to avoid such a problem.

JavaScript in Node.js (just like in the browser) provides a single threaded environment. This means that no two parts of your application run in parallel; instead, concurrency is achieved through the handling of I/O bound operations asynchronously. For example, a request from Node.js to the database engine to fetch some document is what allows Node.js to focus on some other part of the application:

// Trying to fetch an user object from the database. Node.js is free to run other parts of the code from the moment this function is invoked..
db.User.get(userId, function(err, user) {
   // .. until the moment the user object has been retrieved here
})
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22%

If the above situation sounds familiar, then this article is essential for you. If not, you will learn a neat trick with Node.JS that you could use when a situation demands it. So, without further ado, let’s look at how we could compare images and detect duplicates using Node.JS by applying perceptual hashing (pHash) and using the Map data structure.,Generate unique fingerprints for images using perceptual hashing technique.,With the above code, we will be getting an array with the image file names when the promise resolves. for the sake of simplicity, we assume that our directory contains just images.,From here on, we can decide how we’d like to handle duplicates based on the situation and the requirement.

So our hash function is as follows:

const fs = require("fs");
const blockhash = require("blockhash-core");
const {
   imageFromBuffer,
   getImageData
} = require("@canvas/image");

async function hash(imgPath) {
   try {
      const data = await readFile(imgPath);
      const hash = await blockhash.bmvbhash(getImageData(data), 8);
      return hexToBin(hash);
   } catch (error) {
      console.log(error);
   }
}

function readFile(path) {
   return new Promise((resolve, reject) => {
      fs.readFile(path, (err, data) => {
         if (err) reject(err);
         resolve(imageFromBuffer(data));
      });
   });
}

function hexToBin(hexString) {
   const hexBinLookup = {
      0: "0000",
      1: "0001",
      2: "0010",
      3: "0011",
      4: "0100",
      5: "0101",
      6: "0110",
      7: "0111",
      8: "1000",
      9: "1001",
      a: "1010",
      b: "1011",
      c: "1100",
      d: "1101",
      e: "1110",
      f: "1111",
      A: "1010",
      B: "1011",
      C: "1100",
      D: "1101",
      E: "1110",
      F: "1111",
   };
   let result = "";
   for (i = 0; i < hexString.length; i++) {
      result += hexBinLookup[hexString[i]];
   }
   return result;
}
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