Node.js

What is local installation of dependencies?

By default, npm installs any dependency in the local mode. Here local mode refers to the package installation in node_modules directory lying in the folder where Node application is present. Locally deployed packages are accessible via require(). To install a Node project locally following is the syntax.

What is Callback

Callback is an asynchronous equivalent for a function. A callback function is called at the completion of a given task. Node makes heavy use of callbacks. All APIs of Node are written is such a way that they supports callbacks. For example, a function to read a file may start reading file and return the control to execution environment immidiately so that next instruction can be executed. Once file I/O is complete, it will call the callback function while passing the callback function, the content of the file as parameter. So there is no blocking or wait for File I/O. This makes Node.js highly scalable, as it can process high number of request without waiting for any function to return result.

What do you mean by Asynchronous API?

All APIs of Node.js library are aynchronous that is non-blocking. It essentially means a Node.js based server never waits for a API to return data. Server moves to next API after calling it and a notification mechanism of Events of Node.js helps server to get response from the previous API call.

What are the benefits of using Node.js?

Following are main benefits of using Node.js Asynchronous and Event DrivenAll APIs of Node.js library are asynchronous that is non-blocking. It essentially means a Node.js based server never waits for a API to return data. Server moves to next API after calling it and a notification mechanism of Events of Node.js helps server to get response from the previous API call. Very Fast Being built on Google Chrome's V8 JavaScript Engine, Node.js library is very fast in code execution. Single Threaded but highly Scalable − Node.js uses a single threaded model with event looping. Event mechanism helps server to respond in a non-bloking ways and makes server highly scalable as opposed to traditional servers which create limited threads to handle requests. Node.js uses a single threaded program and same program can services much larger number of requests than traditional server like Apache HTTP Server. No Buffering − Node.js applications never buffer any data. These applications simply output the data in chunks.

Name some of the attributes of package.json?

Following are the attributes of Package.json name − name of the package version − version of the package description − description of the package homepage − homepage of the package author − author of the package contributors − name of the contributors to the package dependencies − list of dependencies. npm automatically installs all the dependencies mentioned here in the node_module folder of the package. repository − repository type and url of the package main − entry point of the package keywords − keywords

What is global installation of dependencies?

Globally installed packages/dependencies are stored in <user-directory>/npm directory. Such dependencies can be used in CLI (Command Line Interface) function of any node.js but can not be imported using require() in Node application directly. To install a Node project globally use -g flag.

What is typically the first argument passed to a Node.js callback handler?

Node.js core modules, as well as most of the community-published ones, follow a pattern whereby the first argument to any callback handler is an optional error object. If there is no error, the argument will be null or undefined. A typical callback handler could therefore perform error handling as follows: function callback(err, results) { // usually we'll check for the error before handling results if(err) { // handle error somehow and return } // no error, perform standard callback handling }

What is Node.js?

Node.js is a web application framework built on Google Chrome's JavaScript Engine(V8 Engine). Node.js comes with runtime environment on which a Javascript based script can be interpreted and executed (It is analogus to JVM to JAVA byte code). This runtime allows to execute a JavaScript code on any machine outside a browser. Because of this runtime of Node.js, JavaScript is now can be executed on server as well. Node.js also provides a rich library of various javascript modules which eases the developement of web application using Node.js to great extents. Node.js = Runtime Environment + JavaScript Library

How does Node.js handle child threads?

Node.js, in its essence, is a single thread process. It does not expose child threads and thread management methods to the developer. Technically, Node.js does spawn child threads for certain tasks such as asynchronous I/O, but these run behind the scenes and do not execute any application JavaScript code, nor block the main event loop. If threading support is desired in a Node.js application, there are tools available to enable it, such as the ChildProcess module.

What is REPL? What purpose it is used for?

REPL stands for (READ, EVAL, PRINT, LOOP). Node js comes with bundled REPL environment. This allows for the easy creation of CLI (Command Line Interface) applications. REPL stands for Read Eval Print Loop and it represents a computer environment like a window console or unix/linux shell where a command is entered and system responds with an output. Node.js or Node comes bundled with a REPL environment. It performs the following desired tasks. Read − Reads user's input, parse the input into JavaScript data-structure and stores in memory. Eval − Takes and evaluates the data structure Print − Prints the result Loop − Loops the above command until user press ctrl-c twice.

How does Node.js support multi-processor platforms, and does it fully utilize all processor resources?

Since Node.js is by default a single thread application, it will run on a single processor core and will not take full advantage of multiple core resources. However, Node.js provides support for deployment on multiple-core systems, to take greater advantage of the hardware. The Cluster module is one of the core Node.js modules and it allows running multiple Node.js worker processes that will share the same port.

What is the preferred method of resolving unhandled exceptions in Node.js?

Unhandled exceptions in Node.js can be caught at the Process level by attaching a handler for uncaughtException event. process.on('uncaughtException', function(err) { console.log('Caught exception: ' + err); }); However, uncaughtException is a very crude mechanism for exception handling and may be removed from Node.js in the future. An exception that has bubbled all the way up to the Process level means that your application, and Node.js may be in an undefined state, and the only sensible approach would be to restart everything. The preferred way is to add another layer between your application and the Node.js process which is called the domain. Domains provide a way to handle multiple different I/O operations as a single group. So, by having your application, or part of it, running in a separate domain, you can safely handle exceptions at the domain level, before they reach the Process level.

How to update a dependency using npm?

Update package.json and change the version of the dependency which to be updated and run the following command.

Consider following code snippet: { console.time("loop"); for (var i = 0; i < 1000000; i += 1){ // Do nothing } console.timeEnd("loop"); } The time required to run this code in Google Chrome is considerably more than the time required to run it in Node.js. Explain why this is so, even though both use the v8 JavaScript Engine.

Within a web browser such as Chrome, declaring the variable i outside of any function's scope makes it global and therefore binds it as a property of the window object. As a result, running this code in a web browser requires repeatedly resolving the property i within the heavily populated window namespace in each iteration of the for loop. In Node.js, however, declaring any variable outside of any function's scope binds it only to the module's own scope (not the window object) which therefore makes it much easier and faster to resolve.

What is npm

npm stands for Node Package Manager. npm provides following two main functionalities: Online repositories for node.js packages/modules which are searchable on search.nodejs.org Command line utility to install packages, do version management and dependency management of Node.js packages.

What is Package.json?

package.json is present in the root directory of any Node application/module and is used to define the properties of a package.