Node JS Tutorial

Introduction

Node Js or Node is an open source and cross-platform runtime envirnonment for executing JavaScript code outside of a browser. Quite often we use node to build back-end services also called apis or application programming interfaces, these are the services that power our client apllications like a web app running inside of a web browser or a mobile app on a mobile device. These client apps are simply what the user sees and interact with, They're just the surface they need to talk to some services sitting on the server or in the cloud to store data, send emails or push notifications, kick off workflows,...

Node is ideal for building Highly-scalable, data-intensive and real-time apps/back-end sevices that power our client applications. Now you might ask but there are other tools and frameworks out there for building back-end services such as asp.net, rails & Django,... So what's special about Node?

• Well Node is easy to get started and can be used for prototyping and agile development, but it can also be used for building super fast and highly scalable services. It is used in production by large companies such as PayPal, Uber, Netflix, Walmart,... In fact at PayPal they rebuilt one of their Java and spring based applications using Node Js and they found that the Node application was built twice as fast with fewer people in 33% fewer lines of code and 40% fewer files and more importantly they doubled the number requests served per second while decreasing the average response time by 35%. So Node is an excellent choice for building highly scalable services

• Another reason for using Node is that in old applications we use JavaScript, so if you're a Front-end Developer and know JavaScript you can reuse your JavaScript skills and a Transtion to a Full-stack developer and get a better job with a better pay! You don't have to learn a new programming language also because you can use JavaScript both on the Front-end and on the Back-end your source code will be cleaner and more consistent, so you will use the same naming conventions, the same tools and the same best practices
• And finally another reason for using Node is that it has the largest ecosystem of open source libraries available to you! So for pretty much any features or building blocks you want to add to your application, there is some free open source library out there that you can use. So you don't have to build this building blocks from scratch and instead you can focus on the core of your application.

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Node Architecture

So above we learnt that Node is a runtime environment for executing JavaScript code, but what is a runtime environment really? Well before Node we used JavaScript only to build applications that run inside of a browser, so every browser out there has what we call a JavaScript Engine That takes our JavaScript code and converts it to code that a computer can understand.

• For example Micosoft Edge uses chakra, Firefox uses SpiderMonkey and Chrome uses V8.

• And it's beacause of these varieties of engines that sometimes JavaScript code can behave differently in one browser or another. Now a browserprovides a runtime environment for JavaScript code

• For instance you probably know that in browsers we have the window or the document object, these objects allow us to work with the environment in which our code is running.

document.getElementById('');

• Now up to 2009 the only way to execute JavaScript code was inside of a browser.
  • In 2009 Ryan Dahl the creator of Node came up with a brilliant idea, he thought it would be great to execute JavaScript outside of a browser, so he took Google's V8 Engine which is the fastest JavaScript Engine out there and embedded it inside a C++ program and called that program Node. So similar to a browser Node is a runtime environment for JavaScript code, it contains a JavaScript Engine that can execute our JavaScript code, but it also has certain objects that provide an environment for our JavaScript code. But these objects are different from the environment objects we have in browsers, for example:
    • We don't have the document object, instead we have other objects that give us more interesting capabilities, for example; We can work with file system, listen for requests on a given port,... We can't do stuff like that inside of a browser, right?

browser's object:

document.getElementById('');

Node's objects:

fs.readFile()

http.createServer()

• Ryan Dahl's brilliant idea:

• In essence Node is a program that includes the V8 JavaScript Engine plus some additional modules that give us capabilities not available inside browsers, we can work with the file system or the network,... Both Chrome and Node share the same JavaScript Engine, but they provide different runtime environments for JavaScript.
  • Some people compare Node to C# or Ruby or some other Programming Languages, but these comparisons are fundamentally wrong! Because Node is not a programming language, it's like comparing a car with an apple. By the same token Node should not be compared with frameworks such as ASP.NET or Rails or Django,... These are frameworks for building web applications. Node is not a framework, it's a runtime environment for executing JavaScript code

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How Node works?

Above it's mentioned that Node applications are Highly-scalable and this is because of the Non-blocking or ASYNCHRONOUS nature of Node, what does it mean by ASYNCHRONOUS here is a metaphor; imagine you go to a restaurant a waiter comes to your table takes your order and gives it to the kitchen then they move on to serve another table while the chef is preparing your meal, so the same person can serve many different tables, they don't have to wait for the chef to cook one meal before they serve another table, this is what we call Non-blocking or ASYNCHRONOUS architecture and this is how Node applications work. The waiter is like a thread allocated ho handle a request so a single thread is used to handle multiple requests.

In contrast to Non-blocking or ASYNCHRONOUS architecture we have Blocking or SYNCHRONOUS architecture, let's see how this one works; So back to our restaurant example imagine you go to another restaurant and in that restaurant a waiter is allocated to you, they take your order and give it to the kitchen now they are sitting in the kitchen waiting for the chef to prepare your meal at this time they're not doing anything else, they're just waiting, they're not going to take an order from another table until your meal is ready! This is what we call Blocking or SYNCHRONOUS architecture, and that's how applications built with frameworks like ASP.NET or Rails work out of the box. So when we receive a request on the server a thread is allocated to handle that request, as part of handling that requests it is likely that we're going to query a database and as you know sometimes it may take a little while until the result is ready, when the database is executing the query that thread is sitting there waiting. It can't be used to serve another client, so we need a new thread to serve another client.

• Non-blocking OR ASYNCHRONOUS Architecture

Node.mp4

• Blocking OR SYNCHRONOUS Architecture

Node1.mp4

Now imagine what would happen if we have a large number of concurrent clients, at some point we're going to run out of threads to serve these clients, so new clients have to wait until three threads are available or if we don't want them to wait, we need to add more hardware, So with this kind of architecture we are not utilizing our resources efficiently. This is the problem with Blocking or SYNCHRONOUS architecture and as expalined that's how applications built with frameworks like ASP.NET work by default of course in ASP.NET, it is possible to use ASYNCHRONOUS architecture but you will have to do extra work for now, in contrast Node applications are asynchronous by default, so you don't have to do anything extra.

In Node we have a single thread to handle all requests, when a request arrives that single thread is used to handle that request, if you need to query a database or thread doesn't have to wait for the database to return the data.

While the database is executing our query that thread will be used to serve another client, when the database prepares the result it puts a message in what we call an Event queue.

Node Js is continuously monitoring this queue in the background, when it finds an event in this queue it will take it out and process it, this kind of architecture makes Node ideal for building applications that include a lot of disk or network access.

• We can serve more clients without the need to throw in more hardware and that's why Node applications are Highly-scalable.

• In contrast Node should not be used for CPU-intensive applications like a video encoding or an image manipulation service, in this kind of applications we have a lot of calcuations that should be done by CPU and few operations that touch the file system or the network

• Since Node applications are single threaded when performing the calculation to serve one client other clients have to wait, and that's why Node should not be used for CPU-intensive applications. It should only be used for building data-intensive and real-time applications.