- Ask Nodejs: Delay Firing Socket Io Socket.on(disconnect For Mac Os
- Ask Nodejs: Delay Firing Socket Io Socket.on(disconnect For Mac Free
Question 1: Where can I install Node.js? Answer We can download Node.js software from the. After successful installation look at the installation location, and then you will see the three important parts.
Node This file starts a Node.js JavaScript engine. You can execute any JavaScript file with this node file. npm npm is used for managing the Node.js Package. nodemodule This folder contains the installation Node.js Package. This package acts as a Library.
Verifying Node.js Installation After successful installation of Node.js, you can check if it’s working. Open Command Prompt and write the following command. Question 2: What is Node.js? Answer Node.js is a server-side JavaScript platform which is built on Google Chrome’s JavaScript V8 engine. It is an open source and cross platform application to develop server side and networking applications. Anyone can develop the Node.js application by writing code in JavaScript and it can be run on Microsoft Windows, Linux, or OS X.
Node.js is not a new language and also it is not just a framework built on JavaScript. It is built on Chrome's JavaScript Runtime, so the code is written and executed very similarly to the browser. Features of Node.js Following are some important features of Node.js. Fast in Code execution It is very fast in code execution. Highly scalable Node.js uses a single thread model for event looping. Events respond to the server without blocking other operations. This makes Node.js highly scalable.
One of the big issues with this type of application is latency. You will likely experience a delay of at least 200 ms even over USB. Most people pursuing this type of application are using Unity on a PC and connecting the THETA to the PC with a USB cable.
Traditional servers create limited threads to handle requests and Node.js creates a single thread that provides service to much larger numbers of requests. Event Driven and Asynchronous All API of Node.js are asynchronous.
It means that the server is moving the next API call without waiting for returning data of previous requests. No Buffering Node.js never buffers any data. Many of us are confused about Node.js. It is not a web server like Apache.
Node.js provides a new way to execute our code. It is JavaScript runtime. Node.js provides the facility to create an HTTP server and we can host our application on the same. For more visit the following link,. Question 3: What are the key features of Node.js? Answer Here are the following key features of Node.js:.
Real time Data intensive. Example - Multiplayer Games, Stock Trading, Chat App etc. Highly scalable servers for Web Applications. Example - E-Commerce, Social Media, REST API etc.
Builds fast and scalable network Applications. Example - Proxy Server, Backend web services, HTTP Web Server etc. Node.js main features.
Node.js version 6 focuses on performance improvements, increased reliability and better security for its 3.5 million users. Event driven and Asynchronous. Node.js is emerging as a universal platform used for Web Applications, IoT, mobile, Enterprise Application development and micro service architectures. Full stack JavaScript developers can use it for front end, back end, mobile and IoT projects. Node.js v6 comes equipped with v8 JavaScript engine 5.0, which has improved ECMAScript 2015 (ES6) support. Ninety-three percent of ES6 features are also now supported in the Node.js v6 release.
Single Threaded but highly Scalable. For more visit the following link. Question 4: What are the advantages of Node.js? Answer Node.js is an open source, cross-platform runtime environment for server-side and networking applications. Node.js applications are written in JavaScript and can be run within the Node.jsruntime on OS X, Microsoft Windows, Linux, FreeBSD, NonStop and IBM. Advantages.
Web development is done in a dynamic language (JavaScript) on a VM that is incredibly fast (V8). It is much faster than Ruby, Python, or Perl. Ability to handle thousands of concurrent connections with minimal overhead on a single process. JavaScript is perfect for event loops with first class function objects and closures. People already know how to use it this way having used it in the browser to respond to user-initiated events. Many people already know JavaScript, even people who do not claim to be programmers.
It is arguably the most popular programming language. Using JavaScript on a web server as well as the browser reduces the impedance mismatch between the two programming environments that can communicate data structures via JSON that work the same on both sides of the equation. Duplicate form validation code can be shared between server and client and so on. For more visit the following link. Question 5: Explain REPL in Node.js. Answer The REPL stands for Read Eval Print Loop, which is a simple program that accepts the commands, evaluates the commands, and prints their results. It represents a computer environment like Unix/Linux shell or a window console in which we can enter the command and the system responds with output.
REPL performs the following tasks:. READ Read the input from user, parse it into JavaScript data structure and store it in memory. EVAL Execute the data structure. RINT Print the result.
LOOP Loop the command until user presses Ctrl+C two time. For more visit the following link,. Question 6: What is Closure? Answer Closure is a function defined within another scope that has access to all the variables within the outer scope. A Closure allows us a free environment for the outer function to access the inner functions and inner variables without any scope restrictions. Closure is the local variable for a function, kept alive after the function has returned; or it's a stack-frame that is not deallocated when the function returns.
A Closure is an inner function that has access to the outer function variable's scope chain. The Closure has 3 scope chains; the first one is to access to its own scope (variables defined within the curly brackets) and the second one is to access the outer function's variables and the third one is to access the global variables. Points to remember about Closures,. Whenever you use a function inside another function, a Closure is used. Closure in JavaScript is like keeping a copy of all the local variables.
A Closure is created just on entry to a function and the local variables are added to that Closure. A new set of local variables are kept every time a function with a Closure is called. Closure is the term for both the functions along with the variables that are captured. For more visit the following link,. Question 7: What is NPM? What is the need of NPM in Node.js?
Answer NPM stands for Node.js Package Management. It comes with Node.js platform and allows us to install various packages for Node.js. This package manages and supports various commands to install and remove the modules. Here one important note is we require either package.json file or the nodemodules folder to install modules locally. One of the best things about npm is that it locally stores all dependencies. For example, if module X uses module A version 1.0, and module Y uses module A version 1.5, then both X and Y will have their own local copies of module A.
Need of npm package While I was working on a real node.js application I encountered many instances where I needed to write a few libraries. Recently, I thought these libraries could be useful for others.
Afterward, I discovered the npm package. For more visit the following link,. Question 8: Explain event loop architecture of NodeJS. Answer. When a request arrives, it is queued up into the EventLoop with a JavaScript Closure that includes the event (request, response) and corresponding callback. The event is then given to the one worker thread if the job seems to take a long time to complete, that is from a C Thread Pool, handled by the libuv library.
Once the job is done, the corresponding callback is fired to return back the response to the Main thread. The Event Loop returns the response to the client. Question 9: Explain Node Package Manager. Answer The Node Package Manager is a Command line utility. It allows you to find, install, remove, publish and do a lot of other things related to Node Packaged Modules. The Node package Manager provides a link between the Node Package Registry and development environment.
Node Package Manager lists some of the Command line options. Question 11: Explain some concepts in Node.js. Answer Node.js uses some of the following concepts,. Debugger Statement inserting debugger; in the code of java script it will help to enable break point. Modules Node.js supports simple module loading system. Console Console module provides debugging feature that is similar in Java script console by browser. Streaming By various objects in node js it is abstract interface implemented.
Cluster It allows us to create child process easily that shares server port. DNS DNS module contains functions. Add-ons It is a dynamically linked shared object. Domain It provides a way to handle multiple different IO operations as a single group. Buffer It is similar to array of integers but corresponds to fixed-sized.
Global It is available for all modules. Net It provides asynchronous network wrapper. Call backs It is called when given task will be completed. Error handling It supports various types of categories error.
Crypto It provides cryptographic functionality that includes a set of wrappers for Open SSL’s hash. For more visit the following link,. Question 12: What is Cluster Server Object in Node.JS? Answer A single instance of Node runs in a single thread.
The cluster module allows you to create child processes that all share server ports. When you call server.listen in a worker, it serializes the argument and passes the request to the master process. If the master process already has a listening server matching the worker's requirement, then it passes the handle to the server. If it does not already have a listening server matching that requirement then it will create one and pass the handle to the worker. Cluster Events. fork. online.
listening. disconnect Fork: the fork event is fired when the master attempts to fork a new child; it receives a worker object. Online: the online event is fired when the master receives a notification that the child is fully bound; it receives a worker object. Listening: when the worker performs an action that requires a listen call such as HTTP server. The event emits two arguments, the first one is a worker object, and the address object contains the address, port and address type value of the connection.
Disconnect: called whenever a child is disconnected from the cluster; that can happen either through a process or exit event. For more visit the following link,. Question 13: Why do we use Node.js and how does Node.js work? Answer Node.js is specially designed for building fast, efficient, scalable network applications and uses an event-driven, non-blocking I/O model to maximize efficiency.
The callback function is what Node calls a listener function and it is called by the server whenever a new request comes in. How it works The following describes how Node.js works,. You use your web browser to make a request for 'about.html' on a Node.js web server.
The Node server accepts your request and calls a function to retrieve that file from disk. While the Node server is waiting for the file to be retrieved, it services the next web request. When the file is retrieved, there is a callback function inserted into the Node server's queue. The Node server executes that function that in this case would render the HTML page and send it back to your browser.
Platforms for Node.js. Runs on OSX, Linux, and Windows.
Clickable installer for Windows and MacOSX. For more visit the following link,. Question 14: Explain Process.nextTick function in Node.js. Answer The Process.nextTick function typically runs before any other I/O events fire. As we know, every node application runs on a single thread, in other words only one task or event is processed by Node's event loop. In an event loop, a queue of callbacks are processed by Node on every Tick of the event loop. On the next loop around the event loop calls these callbacks.
The Process.nextTick function defers the function until a completely new stack. You can call as many functions as you want to in the current stack. When the event loop is looking for a new event to execute the nextTick function will be in the queue and will execute an entire new stack. The Process.nextTick function defers the execution of an action until the next pass around the event loop. For more visit the following link,. Question 15: Explain Colors Module in Node.js. Answer The color module uses the popular color.js.
Since the color module is not a built-in module of node.js, we need to install it using the node package manager. Npm install colors Once the command has executed successfully, you will find the following screen. In my case it's showing that the colors module was successfully installed in the application and is ready for use. The beauty of the colors module is that we can beautify the output with various colors. Here is the link to the colors module in NPM. Color Let's implement a few small examples to understand how the colors module works with node.js. Have a look at the following example.
Modules are part of the program. Programs are composed of one or more independently developed modules that are not combined until the programs are linked. The structure of the module is identical to the structure of the program. Node has a simple module loading system. In Node there is a one-to-one correspondence of files and modules. As I have shown you in the example below, Module.js loads the module RequireModule.js in the same directory.
Write the following code in Notepad and save the file with the.jsextention. Now define the module RequireModule.js that is loaded into Module.js, Now open the Node.js command prompt and execute the following code, Now write the following command in the Command Prompt, In the module.js module we have defined the function area.
To add functions and objects to the root of your module you can use the 'exports' object. Variables are in modules as private as though the module was wrapped in a function.
In the example above the variable PI is private to requiremoduel.js. If you want to export an object in one assignment then assign it to 'module.exports' instead of ' exports'. For example, Create a file and save this file with a.js extension as in the following figure, Now create a module in a square.js file as in the following figure, Now in a node.js command prompt execute the module as in the following figure In the example given above you see the bar.js file uses the square module and the square module is defined in Square.js. Core Module The core modules are defined in node's 'lib' folder.
Node has several modules compiled into the binary. Core modules are loaded if their identifier is passed to require.
For more visit the following link,. Question 19: Difference between Node.js and PHP. Answer Node.JS is an environment where you need to do everything yourself. It may sound crazy to you.
The thing is there is no default HTTP server or any other server for the several required purposes. In the node.js environment one script handles all the communication with the respective clients. This considerably reduces the number of resources used by an application. This fact can be overwhelming for a beginner.
Here I am comparing both with an example: Node.JS Code Snippet. obj.emitEvent; In Node we do not have the DOM so we use the EventEmitter class.
This class has mainly two methods, 'on' and 'emit'. I have given the example and sample use of these methods in the NodeJS environment. EventEmitter Class The event module contains the EventEmitter class. The Util package provides the way to inherit from one class to another class. The 'EventEmitter' class allows us to listen for events and assign actions to run when those events occur. The EventEmitter class is based on a publish/subscribe model because we can subscribe to events and then publish them. When we use theEventEmitter class we need to require an events module in the program, for example.
require( 'events' ) Functions can be attached to objects, to be executed when an event is emitted; these function are listeners. Inside a listener function, 'this' refers to the 'EventEmitter' that the listener was attached to.
Features of EventEmitter class,. This class is for managing events. Can be extended to provide event functionality in other classes. It emits events. It listens to and handles those events. Something that drives the two, causing events to be emitted. EventEmitter Methods.
emitobj.on(event, listener). emitobj.emit(event,arg1,arg2.argN). emitobj.once(event, listener). emitobj.removeListener(event, listener) For more visit the following link,. Question 22: Explain Event-Driven Programming in Node.js. Answer Event-Driven Programming is the term where the flow of the code is determined by events (click, load and so on).
It's one of the basic milestones of today's popular programming languages, such as C#, Java and many more; I won't dwell on all of them here. In Node.js and moreover in any kind of JavaScript project, you'll be using or have used event-driven processes.
Whether it's a page on load or a button click event, this is something you have done, whether you knew it or not. Let's make an example to the classic event-driven process and how it's done in NodeJS. Karma runs JavaScript test cases against real browsers through Command Line Interface (CLI) rather than virtual browser and DOM.
Since DOM rendering across browsers vary, for correctness of the test report it uses real browsers. It can configure what browsers need to be used while running Karma. Jasmine Jasmine is a BDD (Behavior Driven Development) Javascript testing framework which provides building blocks to write JavaScript unit test cases. It does not require any other JavaScript Framework. As stated in official documentation of Jasmine 2.0.0, “ Jasmine is a behavior-driven development framework for testing JavaScript code. It does not depend on any other JavaScript frameworks.
It does not require a DOM. And it has a clean, obvious syntax so that you can easily write tests.” Here is a code snippet which describes the basic structure of Jasmine Unit Test Spec. XALT App Bar Button An App bar in XALT can easily be divided into four categories.
These two categories have a different significance but the core functioning is the same in both cases. For more visit the following link,. Question 36: What is Express project and how can you create Express project?
Answer Express is a framework that allows the creation of the MVC web architecture in a Node JS application. There are many ways to create an Express project but in this article I will use Intellij IDEA to create a node Express project. Create Express project Open Intellij IDE and create a new project as in the following: Click on the Finish button and intellij will start downloading the required modules and files for your Express project. Click the ' Configure' button to include the node core library in your project. This core library will help you to enable intelligence when writing node code. Finally our Express project is ready with its predefined structure. An Express project contains many folders and files.
The above structure isn't very hard to understand, let's drill it down. nodemodules An Express project uses a MVC framework and it uses many other modules that we call dependency modules for the Express framework. So all dependency modules are stored in the nodemodules folder.
public This folder contain CSS, JavaScript files and images. routes This folder contains a JS file that will help to route user URL. In this folder we can create many JS files and use them in an app.js file. views This is the folder where we add our jade page. This jade page will be shown in the browser. app.js This file is the heart of the Express framework.
In this file we configure the Express application settings. package.json It is a JSON configuration file where we can configure project details and its dependencies For more visit the following link,. Question 37: What is Asynchronous Programming? Answer Every function in node.js is asynchronous which means that everything that would normally block the thread is instead executed in the background, in other words it continues running in the background and the flow of control moves to the next line and executes them; the moment the operation is completed it executes a callback that will then be executed. For example if you are reading a file on the file system then you need to specify a callback function that is executed when the read operation has completed. For more visit the following link,. Question 38: What is middleware?
Answer Middleware is actually a very simple concept to understand, it is very similar to middleman. What middleman does is he takes the request from one party and gets in touch with the other party, he does what needs to be done and then provides a response back to the party which placed the request in the first place. So middleware are just simple functions with three arguments; request, response and next, they act as a middleman; when express receives a request, express passes this request to each middleware in the chain until it receives a response.
In general, there are two kinds of middleware, first one being a normal middleware, and the second one an error handling middleware. Middleware concept is at the core of express.js and very important to understand, almost everything in express.js is a middleware, from body parsers to loggers, from routes to error handlers.
So it is very important to understand what are middlewares and how they work. A middleware has the following signature. var mqtt = require( 'mqtt' ).
var fs = require( 'fs' ). var broker = 'mqtt://test.mosquitto.org'. var client = mqtt.connect(broker). var forecast = fs.readFileSync( './forecast.json' ).toString;. client.publish( 'mydevice/forecast', forecast).
client.end;. console.log( 'Successful!'
); In order to run the server program, just key in “ node server.js” and hit enter. The following is the snapshot of the program running on node.js. Key thing about MQTT broker You can find more information on There’s a provision to set up our own MQTT server and make use of it too. For more visit the following link,. Question 43: How can you use Node.js and Angular JS with SQL Server? Answer Installation requirements for this:.
Ask Nodejs: Delay Firing Socket Io Socket.on(disconnect For Mac Os
Install. Install Visual Studio 2012. Install SQL Server 2008 r2.
NTVS 1.0. Use Angular js library Procedure Create a table in your database and insert a row as in the following.
INSERT INTO IMS1.0.dbo.Nodejs. (Text). VALUES. ( 'Hello word!!' ). GO Open the project in Visual Studio and you will see the following folder structure, How to install all packages Right-click on npm and select Install New npm Packages.
Open the api.js file and set the Microsoft SQL database credentials and database name. Enter the following query, Please download the code and use the following procedure and run the code. Output Window, For more visit the following link,. Question 44: What are the popular modules of NPM in Node.js? Answer is an online module repository (kind of like Play Store for Node module) that allows you to use publicly available and reusable modules with version and dependency management.
Popular modules are,. Express.js. Connect. Socket.io. Jade. Mongodb.
Redis. Coffee-script. Underscore For more visit the following link,. Question 45: How can you read Files Using Fs? Answer When you look at the node.js documentation you will find the file system module. There you will find several functions and we will use one of them. Code So, start from the first line of code.
Fs is a variable for storing a reference of the file-system. In JavaScript we use the require function to include an external module.
Then, we need a callback function that will show your text-file content. So, it takes two arguments, error and data, where data is your content. Thus, we have used the console.log function to show your content. And next we have the readFile function that takes two arguments. First will be your resource-file's path and the second will be your callback function. And finally, we have written another print statement so that we can see the non-block nature of node.
Before we move to the explanation part: Output As we can see, ' Continue' is in the beginning and then we have the contents of the text file. That is just because node starts executing the code and when it gets to the readFile function it doesn't stop there, else it moves to the next statement (non-blocking state) and when reading is completed it gets called to print the output. That's why we call those function as callback functions. For more visit the following link,. Question 46: How can you handleJSON Files in Node.JS?
Answer JSON is a file format that is very reliable when transacting using APIs. And node plays a vital role in giving JSON a new makeover. Or, you can say it's a better alternative to XML. We will read the file synchronously. The JSON file is among those files that supports synchronous calls.
So, first we need a dummy JSON file. And save it as sample.json. Whereas, the dummy text file would be like: Save it as demo.txt. Code First, we will deal with the synchronous call.
It's a conventional way of reading any file. Either in C or PHP, they manage files synchronously. By synchronous, I mean one-way execution where you have a single-flow that executes line-by-line and it will move to the next statement when the statement completes. Unlike an asynchronous call, flow-control moves to the next line without showing any concern over its completion. And, after completion it will call the specified callback function. This shows the vital difference between blocking (synchronous) and non-blocking (asynchronous) calls.
So, let's explore synchronous calls. And, the synchronous output will be like we expect always (single-flow). So, there is nothing new in it. But, when we read any JSON file then we can manipulate more. And filter the content of the file.
Every time, you must use the synchronous way when you are dealing with a JSON file. And the output will be like: Conclusion Keeping a constant value in a JSON file is always a good idea. Suppose you are setting a server and you are asked to maintain the credentials of the server. Then you put those credentials in a JSON file, so you can change it in the future.
For more visit the following link,. Question 47: How can you cast a simple spell in Node.js? Answer Let's install the Node.js now via. After completing the installation open the “ Node.js” application with the Green icon to start casting your spells. Let's say we want to write “ Poooof” on the console, here is how. console.log( 'Poooff' ); For more visit the following link,.
Question 48: What are the key points of Node.js? Answer These are the key points about Node.js,.
Node.js is nothing but server-side JavaScript. Single-threaded environment. Asynchronous event driven server-side JavaScript. Runs on Google JS ver-8 Engine.
Ask Nodejs: Delay Firing Socket Io Socket.on(disconnect For Mac Free
Non blocking I/O and File API. Highly scalable. Nodes apps are created. Achieving Scale and Concurrency. Written in C and C.
A file in node.js is called a Module. High performance. For more visit the following link,. Question 49: How can you Implement Visitor Counter in Node.js? Answer We would just like to implement a simple hit count for our web server.
For example, we know that in ASP.NET application variables are globally shareable and static in nature, in other words if a user changes a value then all users will see the changed version. In our example we will count the number of hits in our web server. Have a look at the following code.
Yes, I know that there are already thousands of similar questions - And no, none of the answers have worked for me. I already had a problem with upgrading my Angular quite some while ago, and just decided to ignore the new updates.