28+ Full Stack Developer Interview Questions (ANSWERED for 2020)

DevOps is a newly emerging term in IT field, which is nothing but a practice that emphasizes the collaboration and communication of both software developers and other information-technology (IT) professionals. It focuses on delivering software product faster and lowering the failure rate of releases.

• Maintain a code repository
• Automate the build
• Make the build self-testing
• Everyone commits to the baseline every day
• Every commit (to baseline) should be built
• Keep the build fast
• Test in a clone of the production environment
• Make it easy to get the latest deliverables
• Everyone can see the results of the latest build
• Automate deployment

Asynchronous JavaScript, or JavaScript that uses callbacks, is hard to get right intuitively. A lot of code ends up looking like this:

fs.readdir(source, function (err, files) {
  if (err) {
    console.log('Error finding files: ' + err)
  } else {
    files.forEach(function (filename, fileIndex) {
      console.log(filename)
      gm(source + filename).size(function (err, values) {
        if (err) {
          console.log('Error identifying file size: ' + err)
        } else {
          console.log(filename + ' : ' + values)
          aspect = (values.width / values.height)
          widths.forEach(function (width, widthIndex) {
            height = Math.round(width / aspect)
            console.log('resizing ' + filename + 'to ' + height + 'x' + height)
            this.resize(width, height).write(dest + 'w' + width + '_' + filename, function(err) {
              if (err) console.log('Error writing file: ' + err)
            })
          }.bind(this))
        }
      })
    })
  }
})

See the pyramid shape and all the }) at the end? This is affectionately known as callback hell.

The cause of callback hell is when people try to write JavaScript in a way where execution happens visually from top to bottom. Lots of people make this mistake! In other languages like C, Ruby or Python there is the expectation that whatever happens on line 1 will finish before the code on line 2 starts running and so on down the file.

In the simplest terms, git pull does a git fetch followed by a git merge.

• When you use pull, Git tries to automatically do your work for you. It is context sensitive, so Git will merge any pulled commits into the branch you are currently working in. pull automatically merges the commits without letting you review them first. If you don’t closely manage your branches, you may run into frequent conflicts.

• When you fetch, Git gathers any commits from the target branch that do not exist in your current branch and stores them in your local repository. However, it does not merge them with your current branch. This is particularly useful if you need to keep your repository up to date, but are working on something that might break if you update your files. To integrate the commits into your master branch, you use merge.

Gitflow workflow employs two parallel long-running branches to record the history of the project, master and develop:

• Master - is always ready to be released on LIVE, with everything fully tested and approved (production-ready).
• Hotfix - Maintenance or “hotfix” branches are used to quickly patch production releases. Hotfix branches are a lot like release branches and feature branches except they're based on master instead of develop.

• Develop - is the branch to which all feature branches are merged and where all tests are performed. Only when everything’s been thoroughly checked and fixed it can be merged to the master.
• Feature - Each new feature should reside in its own branch, which can be pushed to the develop branch as their parent one.

• Docker a low overhead way to run virtual machines on your local box or in the cloud. Although they're not strictly distinct machines, nor do they need to boot an OS, they give you many of those benefits.
• Docker can encapsulate legacy applications, allowing you to deploy them to servers that might not otherwise be easy to setup with older packages & software versions.
• Docker can be used to build test boxes, during your deploy process to facilitate continuous integration testing.
• Docker can be used to provision boxes in the cloud, and with swarm you can orchestrate clusters too.

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.

'use strict' is a statement used to enable strict mode to entire scripts or individual functions. Strict mode is a way to opt into a restricted variant of JavaScript.

Advantages:

• Makes it impossible to accidentally create global variables.
• Makes assignments which would otherwise silently fail to throw an exception.
• Makes attempts to delete undeletable properties throw (where before the attempt would simply have no effect).
• Requires that function parameter names be unique.
• this is undefined in the global context.
• It catches some common coding bloopers, throwing exceptions.
• It disables features that are confusing or poorly thought out.

Disadvantages:

• Many missing features that some developers might be used to.
• No more access to function.caller and function.arguments.
• Concatenation of scripts written in different strict modes might cause issues.

Overall, I think the benefits outweigh the disadvantages, and I never had to rely on the features that strict mode blocks. I would recommend using strict mode.

Let's first look at example of each:

// ES5 Function Constructor
function Person(name) {
  this.name = name;
}

// ES6 Class
class Person {
  constructor(name) {
    this.name = name;
  }
}

For simple constructors, they look pretty similar.

The main difference in the constructor comes when using inheritance. If we want to create a Student class that subclasses Person and add a studentId field, this is what we have to do in addition to the above.

// ES5 Function Constructor
function Student(name, studentId) {
  // Call constructor of superclass to initialize superclass-derived members.
  Person.call(this, name);

  // Initialize subclass's own members.
  this.studentId = studentId;
}

Student.prototype = Object.create(Person.prototype);
Student.prototype.constructor = Student;

// ES6 Class
class Student extends Person {
  constructor(name, studentId) {
    super(name);
    this.studentId = studentId;
  }
}

It's much more verbose to use inheritance in ES5 and the ES6 version is easier to understand and remember.

Both are ways to implement a module system, which was not natively present in JavaScript until ES2015 came along. CommonJS is synchronous while AMD (Asynchronous Module Definition) is obviously asynchronous. CommonJS is designed with server-side development in mind while AMD, with its support for asynchronous loading of modules, is more intended for browsers.

I find AMD syntax to be quite verbose and CommonJS is closer to the style you would write import statements in other languages. Most of the time, I find AMD unnecessary, because if you served all your JavaScript into one concatenated bundle file, you wouldn't benefit from the async loading properties. Also, CommonJS syntax is closer to Node style of writing modules and there is less context-switching overhead when switching between client side and server side JavaScript development.

I'm glad that with ES2015 modules, that has support for both synchronous and asynchronous loading, we can finally just stick to one approach. Although it hasn't been fully rolled out in browsers and in Node, we can always use transpilers to convert our code.

Generally speaking, the event loop is a mechanism that waits for and dispatches events or messages in a program. In Node.js, event loops are the central control flow constructs. For example, every time a request is about to be handled, it’s put on the event loop and processed as soon as it’s ready to be processed. Node, instead of doing it on its own, delegates the responsibility of handling the system. Because of such behaviour, Node is not actively waiting for this task to finish and can handle other requests in the meantime. The event loop makes Node.js faster and more efficient than other technologies

Above code will output undefined as output. delete operator is used to delete a property from an object. Here x is an object which has foo as a property and from self-invoking function we are deleting foo property of object x and after deletion we are trying to reference deleted property foo which result undefined.

The event loop is what allows Node.js to perform non-blocking I/O operations — despite the fact that JavaScript is single-threaded — by offloading operations to the system kernel whenever possible.

Every I/O requires a callback - once they are done they are pushed onto the event loop for execution. Since most modern kernels are multi-threaded, they can handle multiple operations executing in the background. When one of these operations completes, the kernel tells Node.js so that the appropriate callback may be added to the poll queue to eventually be executed.

• 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.