What is Node.js? [closed]

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90%

Emulating private methods with closures,A closure is the combination of a function bundled together (enclosed) with references to its surrounding state (the lexical environment). In other words, a closure gives you access to an outer function’s scope from an inner function. In JavaScript, closures are created every time a function is created, at function creation time.,Those three public functions are closures that share the same lexical environment. Thanks to JavaScript's lexical scoping, they each have access to the privateCounter variable and the changeBy function.,In previous examples, each closure had its own lexical environment. Here though, there is a single lexical environment that is shared by the three functions: counter.increment, counter.decrement, and counter.value.

function init() {
   var name = 'Mozilla'; // name is a local variable created by init
   function displayName() { // displayName() is the inner function, a closure
      alert(name); // use variable declared in the parent function
   }
   displayName();
}
init();
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When running a program in the console you can close it with ctrl-C, but what we want to discuss here is programmatically exiting.,There are various ways to terminate a Node.js application.,You can send this signal from inside the program, in another function:,By default the exit code is 0, which means success. Different exit codes have different meaning, which you might want to use in your own system to have the program communicate to other programs.

If this is fine for you, you can pass an integer that signals the operating system the exit code:

JScopyprocess.exit(1)
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72%

app.listen() returns http.Server. You should invoke close() on that instance and not on app instance., By clicking “Accept all cookies”, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. ,Connect and share knowledge within a single location that is structured and easy to search.,You can still achieve the same by assigning the result of app.listen() function and apply close on it:

Ex.

app.get(
   '/auth/github/callback',
   passport.authenticate('github', {
      failureRedirect: '/login'
   }),
   function(req, res) {
      res.redirect('/');

      setTimeout(function() {
         server.close();
         // ^^^^^^^^^^^
      }, 3000)
   }
);

var server = app.listen('http://localhost:5000/');
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65%

'SIGBREAK' is delivered on Windows when Ctrl+Break is pressed. On non-Windows platforms, it can be listened on, but there is no way to send or generate it.,'SIGKILL' cannot have a listener installed, it will unconditionally terminate Node.js on all platforms.,'SIGTERM' is not supported on Windows, it can be listened on.,'SIGWINCH' is delivered when the console has been resized. On Windows, this will only happen on write to the console when the cursor is being moved, or when a readable tty is used in raw mode.

When iterating over process.allowedNodeEnvironmentFlags, flags will appear only once; each will begin with one or more dashes. Flags passed through to V8 will contain underscores instead of non-leading dashes:

import {
   allowedNodeEnvironmentFlags
} from 'process';

allowedNodeEnvironmentFlags.forEach((flag) => {
   // -r
   // --inspect-brk
   // --abort_on_uncaught_exception
   // ...
});
const {
   allowedNodeEnvironmentFlags
} = require('process');

allowedNodeEnvironmentFlags.forEach((flag) => {
   // -r
   // --inspect-brk
   // --abort_on_uncaught_exception
   // ...
});
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The fs.close() method is used to asynchronously close the given file descriptor thereby clearing the file that is associated with it. This will allow the file descriptor to be reused for other files. Calling fs.close() on a file descriptor while some other operation is being performed on it may lead to undefined behavior.,fd: It is an integer that denotes the file descriptor of the file for which to be closed.,Example 2: This example shows the closing of a file descriptor and trying to access that closed file descriptor again.,callback: It is a function that would be called when the method is executed.err: It is an error that would be thrown if the method fails.

Syntax:

fs.close(fd, callback)

Output:

The file descriptor is: 3

   >
   File Closed successfully

Output:

The file descriptor is: 3

   >
   Finding the stats of the file
Stats of the file generated

   >
   Closing the file descriptor
File Closed successfully

   >
   Finding the stats of the file again
Cannot find stats of file Error: EBADF: bad file descriptor, fstat
at Object.fstatSync(fs.js: 897: 3)
at G: \tutorials\ nodejs - fs - close\ index.js: 42: 23
at FSReqCallback.oncomplete(fs.js: 146: 23) {
   fd: 3,
   errno: -4083,
   syscall: 'fstat',
   code: 'EBADF'
}
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Closure is one of important concept in JavaScript. It is widely discussed and still confused concept. Let's understand what the closure is. , JavaScript - if condition , Closure is valid in multiple levels of inner functions. , Advanced JavaScript

function OuterFunction() {

   var outerVariable = 1;

   function InnerFunction() {
      alert(outerVariable);
   }

   InnerFunction();
}
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fs.open(filePath, 'r', function(err, fd) {
   if (err) {
      return callback(err, false);
   }
   fs.read(fd, _buf, 0, 10, 0, function(err, bytesRead, buffer) {
      fs.close(fd, function() {
         callback(err, (buffer.slice(0, 2).toString() === 'PK'));
      });
   });
});
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