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Basic MEAN Stack Interview Questions and Answers for IT Professionals which would be useful for anyone who is preparing for MEAN Stack Interviews.
For any help on MEAN Stack Certification Training in Chennai.
The term MEAN stack refers to a collection of JavaScript-based technologies used to develop web applications. MEAN is an acronym for MongoDB, ExpressJS, AngularJS, and Node.js. From client to server to database, MEAN is full stack JavaScript.
Express is one the most prevalent and generally utilized web systems in Node.js advancement zone. Express is a negligible web server based on Node.js that gives all the basic features required to handle web applications to the program and cell phones. ExpressJS enables you to deal with Routes, Server, and I/O stuff effortlessly.
Consistent Style helps team members modify projects easily without having to get used to a new style every time. Tools that can help include Standard and ESLint.
The REPL stands for “Read Eval Print Loop”. It is a simple program that accepts the commands, evaluates them, and finally prints the results. REPL provides an environment similar to that of Unix/Linux shell or a window console, in which we can enter the command and the system, in turn, responds with the output. REPL performs the following tasks.
The most common types of IDE’s that can be used for Node.JS development applications are:
OneTime Setup
npm
install -g @angular/cli
ng
new projectFolder
creates
a new applicationBundling Step
ng
build --prod
(run
in command line when directory is projectFolder
)prod
_bundle for productionbundles are generated by default to projectFolder/dist/
Deployment
You can get a preview of your application using the ng serve --prod
command that starts a local HTTP server such that the application with production files is accessible.
For a production usage,
you have to deploy all the files from the dist
folder in the
HTTP server of your choice.
Tree-shakeable providers – a new, recommended, way to register a provider, directly inside the @Injectable() decorator, using the new providedIn
attribute.
RxJS 6 – Angular 6 now uses RxJS 6 internally, and requires you to update your application also. RxJS released a library called rxjs-compat, that allows you to bump RxJS to version 6.0.
ElementRef<T>
– ElementRef had its nativeElement property typed as any. In Angular 6.0, you can now type ElementRef more strictly.
Animations – The polyfill web-animations-js is not necessary anymore for animations in Angular 6.0, except if you are using the AnimationBuilder.
i18n – possibility to have “runtime i18n”, without having to build the application once per locale.
Following is the code snippet to fetch Post Data using Node.js.
app.use(express.bodyParser());
app.post(‘/’, function(request, response){
console.log(request.body.user);
});
Following code snippet can be used to make a Post Request in Node.js.
var request = require(‘request’);
request.post(
‘http://www.example.com/action’,
{ form: { key: ‘value’ } },
function (error, response, body) {
if (!error && response.statusCode == 200) {
console.log(body)
}
}
);
Angular.JS is a web application development framework while Node.js is a runtime system
Mongoose is an Object Document Mapper (ODM). This means that Mongoose allows you to define objects with a strongly-typed schema that is mapped to a MongoDB document.
Operation errors are not bugs, but problems with the system, like request timeout or hardware failure. On the other hand programmer errors are actual bugs.
Callback hell is heavily nested callbacks which make the code unreadable and difficult to maintain.
Let’s see an example below.
downloadPhoto(‘http://onlinebags.com/bag.gif’, displayPhoto)
function displayPhoto (error, photo) {
if (error) console.error(‘Loading error!’, error)
else console.log(‘Loading finished’, photo)
}
console.log(‘Loading started’)
Node.js first declares the “displayPhoto” function. After that, it calls the “downloadPhoto” function and pass the “displayPhoto” function as its callback. Finally, the code prints ‘Download started’ on the console. The “displayPhoto” will be executed only after “downloadPhoto” completes the execution of all its tasks.
Node.js internally uses a single-threaded event loop to process queued events. But this approach may lead to blocking the entire process if there is a task running longer than expected.
Node.js addresses this problem by incorporating callbacks also known as higher-order functions. So whenever a long-running process finishes its execution, it triggers the callback associated. With this approach, it can allow the code execution to continue past the long-running task.
However, the above solution looks extremely promising. But sometimes, it could lead to complex and unreadable code. More the number of callbacks, longer the chain of returning callbacks would be.
There are four solutions which can address the callback hell problem.
It proposes to split the logic into smaller modules. And then join them together from the main module to achieve the desired result.
Promises give an alternate way to write async code. They either return the result of execution or the error/exception. Implementing promises requires the use of <.then()> function which waits for the promise object to return. It takes two optional arguments, both functions. Depending on the state of the promise only one of them will get called. The first function call proceeds if the promise gets fulfilled. However, if the promise gets rejected, then the second function will get called.
Generators are lightweight routines, they make a function wait and resume via the yield keyword. Generator functions uses a special syntax <function* ()>. They can also suspend and resume asynchronous operations using constructs such as promises or <thunks> and turn a synchronous code into asynchronous .
The Angular Ahead-of-Time compiler pre-compiles application components and their templates during the build process. Apps compiled with AOT launch faster for several reasons.
Redux is a way to manage application state and it offers a single source of truth for the application state, and a unidirectional flow of data change in the application. ngrx/store
is one implementation of Redux principles.
Events module in Node.js allows us to create and handle custom events. The Event module contains “EventEmitter” class which can be used to raise and handle custom events. It is accessible via the following code.
// Import events module
var events = require(‘events’);
// Create an eventEmitter object
var eventEmitter = new events.EventEmitter();
When an EventEmitter instance encounters an error, it emits an “error” event. When a new listener gets added, it fires a “newListener” event and when a listener gets removed, it fires a “removeListener” event.
EventEmitter provides multiple properties like “on” and “emit”. The “on” property is used to bind a function to the event and “emit” is used to fire an event.
Stream in Node.js are objects that allows to read data from a source or write data to a specific destination in a continuous fashion. In Node.js, there are four types of streams.
All the streams, discussed above are an instance of an “EventEmitter” class. The event thrown by the Stream varies with time. Some of the commonly used events are as follows.
Following is the list of some of the most commonly used REPL commands.
NPM stands for Node Package Manager. It has two main features.
NPM comes bundled along with Node.js installable. We can verify its version using the following command-
$ npm –version
NPM helps to install any Node.js module using the following command.
$ npm install <Module Name>
For example, following is the command to install a famous Node.js web framework module called express-
$ npm install express
A grid system is a structure that allows for content to be stacked both vertically and horizontally in a consistent and easily manageable fashion. Grid systems include two key components: rows and columns.
A linear search looks down a list, one item at a time, without jumping. In complexity terms, this is an O(n)
search – the time taken to search the list gets bigger at the same rate as the list does.
A binary search is when you start with the middle of a sorted list, and see whether that’s greater than or less than the value you’re looking for, which determines whether the value is in the first or second half of the list. Jump to the half way through the sublist, and compare again etc. In complexity terms this is an O(log n)
search – the number of search operations grows more slowly than the list does, because you’re halving the “search space” with each operation.
It is interesting to note that a Node.Js application facilitates the creation of a single thread when it is activated. Whenever the Node.Js receives a request, it first completes the processing before moving onto the next request processing. It is also important to mention here that Node.Js works by using the event loop.
It also uses call back functions and handles multiple requests that are coming from the user. In the working procedure of Node.Js, an event loop always plays an essential role. An event loop is also known as a function which instigates all the event handlers. Hence, lots of works are done on the back-end. It is also important to note that while processing a request, Node.Js usually attaches a call back function. When the response is ready, the event triggers the callback function to send the response to the queries of the user.
In node.js, “non-blocking” implies that its IO is non-blocking. Hub utilizes “libuv” to deal with its IO in a stage rationalist manner. On windows, it utilizes finish ports for UNIX it utilizes epoll or kqueue and so on. Along these lines, it makes a non-blocking demand and upon a demand, it lines it inside the occasion circle which call the JavaScript ‘callback’ on the fundamental JavaScript string.
Dependency injection makes it easy to create loosely coupled components, which typically means that components consume functionality defined by interfaces without having any first-hand knowledge of which implementation classes are being used.
It makes it easier to change the behavior of an application by changing the components that implement the interfaces that define application features. It also results in components that are easier to isolate for unit testing.
The most popular DevOps tools are:
Containerisation is a type of virtualization strategy that emerged as an alternative to traditional hypervisor-based virtualization.
In containerization, the operating system is shared by the different containers rather than cloned for each virtual machine. For example Docker provides a container virtualization platform that serves as a good alternative to hypervisor-based arrangements.
In Blue Green Deployment, you have two complete environments. One is Blue environment which is running and the Green environment to which you want to upgrade. Once you swap the environment from blue to green, the traffic is directed to your new green environment. You can delete or save your old blue environment for backup until the green environment is stable.
In Rolling Deployment, you have only one complete environment. The code is deployed in the subset of instances of the same environment and moves to another subset after completion.
The main and most important difference between REST and GraphQL is that GraphQL is not dealing with dedicated resources, instead everything is regarded as a graph and therefore is connected and can be queried to app exact needs.
SQL databases store data in form of tables, rows, columns and records. This data is stored in a pre-defined data model which is not very much flexible for today’s real-world highly growing applications. MongoDB in contrast uses a flexible structure which can be easily modified and extended.
Indexes support the efficient execution of queries in MongoDB. Without indexes, MongoDB must perform a collection scan, i.e. scan every document in a collection, to select those documents that match the query statement. If an appropriate index exists for a query, MongoDB can use the index to limit the number of documents it must inspect.
Aggregations operations process data records and return computed results. Aggregation operations group values from multiple documents together, and can perform a variety of operations on the grouped data to return a single result. MongoDB provides three ways to perform aggregation:
If application has to wait for some I/O operation in order to complete its execution any further then the code responsible for waiting is known as blocking code.
yield
with Generators and/or PromisesWe use classes as object factories. A class defines a blueprint of what an object should look like and act like and then implements that blueprint by initialising class properties and defining methods. Classes are present throughout all the phases of our code.
Unlike classes, an interface is a virtual structure that only exists within the context of TypeScript. The TypeScript compiler uses interfaces solely for type-checking purposes.
A class may define a factory or a singleton by providing initialisation to its properties and implementation to its methods, an interface is simply a structural contract that defines what the properties of an object should have as a name and as a type.
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