Node.js Flashcards
What is npm?
Node Package Manager
- provides online repositories for node.js packages/modules
- command line utility to install packages, do version management and dependency management
What is Node.js?
Node.js comes with runtime environment which 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.
What are the two types of API functions in Node.js?
The two types of API functions in Node.js are: a) Asynchronous, non-blocking functions b) Synchronous, blocking functions
What is an error-first callback?
Error-first callbacks are used to pass errors and data. The first argument is always an error object that the programmer has to check if something went wrong. Additional arguments are used to pass data.
What is Callback Hell?
The asynchronous function requires callbacks as a return parameter. When multiple asynchronous functions are chained together then callback hell situation comes up.
What is control flow function?
It is a generic piece of code which runs in between several asynchronous function calls is known as control flow function.
What are Event Listeners?
Event Listeners are similar to call back functions but are associated with some event. For example when a server listens to http request on a given port a event will be generated and to specify http server has received and will invoke corresponding event listener. Basically, Event listener’s are also call backs for a corresponding event.
Node.js has built in event’s and built in event listeners. Node.js also provides functionality to create Custom events and Custom Event listeners.
If Node.js is single threaded then how it handles concurrency?
Node provides a single thread to programmers so that code can be written easily and without bottleneck. Node internally uses multiple POSIX threads for various I/O operations such as File, DNS, Network calls etc.
When Node gets I/O request it creates or uses a thread to perform that I/O operation and once the operation is done, it pushes the result to the event queue. On each such event, event loop runs and checks the queue and if the execution stack of Node is empty then it adds the queue result to execution stack.
This is how Node manages concurrency.
Could we run an external process with Node.js?
Yes. Child process module enables us to access operating system functionaries or other apps. Scalability is baked into Node and child processes are the key factors to scale our application. You can use child process to run system commands, read large files without blocking event loop, decompose the application into various “nodes” (That’s why it’s called Node).
Child process module has following three major ways to create child processes –
spawn - child_process.spawn launches a new process with a given command.
exec - child_process.exec method runs a command in a shell/console and buffers the output.
fork - The child_process.fork method is a special case of the spawn() to create child processes.
What are the key features of Node.js?
Asynchronous event driven IO helps concurrent request handling – All APIs of Node.js are asynchronous. This feature means that if a Node receives a request for some Input/Output operation, it will execute that operation in the background and continue with the processing of other requests. Thus it will not wait for the response from the previous requests.
- Fast in Code execution – Node.js uses the V8 JavaScript Runtime engine, the one which is used by Google Chrome. Node has a wrapper over the JavaScript engine which makes the runtime engine much faster and hence processing of requests within Node.js also become faster.
- Single Threaded but Highly Scalable – Node.js uses a single thread model for event looping. The response from these events may or may not reach the server immediately. However, this does not block other operations. Thus making Node.js highly scalable. Traditional servers create limited threads to handle requests while Node.js creates a single thread that provides service to much larger numbers of such requests.
- Node.js library uses JavaScript – This is another important aspect of Node.js from the developer’s point of view. The majority of developers are already well-versed in JavaScript. Hence, development in Node.js becomes easier for a developer who knows JavaScript.
- There is an Active and vibrant community for the Node.js framework – The active community always keeps the framework updated with the latest trends in the web development.
- No Buffering – Node.js applications never buffer any data. They simply output the data in chunks.
What is the difference between Nodejs, AJAX, and jQuery?
The one common trait between Node.js, AJAX, and jQuery is that all of them are the advanced implementation of JavaScript. However, they serve completely different purposes.
Node.js –It is a server-side platform for developing client-server applications. For example, if we’ve to build an online employee management system, then we won’t do it using client-side JS. But the Node.js can certainly do it as it runs on a server similar to Apache, Django not in a browser.
AJAX (aka Asynchronous Javascript and XML) –It is a client-side scripting technique, primarily designed for rendering the contents of a page without refreshing it. There are a no. of large companies utilizing AJAX such as Facebook and Stack Overflow to display dynamic content.
jQuery –It is a famous JavaScript module which complements AJAX, DOM traversal, looping and so on. This library provides many useful functions to help in JavaScript development. However, it’s not mandatory to use it but as it also manages cross-browser compatibility, so can help you produce highly maintainable web applications.
What are the core modules of Node.js?
- EventEmitter
- Stream
- FS
- Net
- Global Objects
What is global installation of dependencies?
Globally installed packages/dependencies are stored in /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 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?
- Aynchronous and Event Driven - 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.
- 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.
